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 $184.50   12.324%   $207.2378   $207.24   $207.25   $207.20  
  Purchase #2 $44.29   5.669%   $46.8008   $46.80   $46.80   $46.80  
  Purchase #3 $84.28   4.311%   $87.9133   $87.91   $87.90   $87.90  
  Purchase #4 $231.48   3.191%   $238.8665   $238.87   $238.85   $238.90  
  Purchase #5 $6.77   4.586%   $7.0805   $7.08   $7.10   $7.10  
  Purchase #6 $183.59   3.550%   $190.1074   $190.11   $190.10   $190.10  
  Purchase #7 $231.63   9.316%   $253.2087   $253.21   $253.20   $253.20  
  7 purchase totals = $966.54       $1,031.2150   $1,031.22   $1,031.20   $1,031.20