Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $144.64   12.747%   $163.0773   $163.08   $163.10   $163.10  
  Purchase #2 $201.33   4.727%   $210.8469   $210.85   $210.85   $210.80  
  Purchase #3 $175.41   13.586%   $199.2412   $199.24   $199.25   $199.20  
  Purchase #4 $207.81   13.737%   $236.3569   $236.36   $236.35   $236.40  
  Purchase #5 $239.27   10.219%   $263.721   $263.72   $263.70   $263.70  
  Purchase #6 $206.80   12.428%   $232.5011   $232.50   $232.50   $232.50  
  Purchase #7 $159.34   5.864%   $168.6837   $168.68   $168.70   $168.70  
  7 purchase totals = $1,334.60       $1,474.4281   $1,474.43   $1,474.45   $1,474.40