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 $221.76   6.428%   $236.0147   $236.01   $236.00   $236.00  
  Purchase #2 $100.92   5.535%   $106.5059   $106.51   $106.50   $106.50  
  Purchase #3 $53.88   9.794%   $59.157   $59.16   $59.15   $59.20  
  Purchase #4 $186.32   9.385%   $203.8061   $203.81   $203.80   $203.80  
  Purchase #5 $178.36   8.484%   $193.4921   $193.49   $193.50   $193.50  
  Purchase #6 $191.34   5.466%   $201.7986   $201.80   $201.80   $201.80  
  Purchase #7 $50.27   4.203%   $52.3828   $52.38   $52.40   $52.40  
  7 purchase totals = $982.85       $1,053.1572   $1,053.16   $1,053.15   $1,053.20