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 $112.70   5.868%   $119.3132   $119.31   $119.30   $119.30  
  Purchase #2 $35.70   6.302%   $37.9498   $37.95   $37.95   $37.90  
  Purchase #3 $234.32   13.311%   $265.5103   $265.51   $265.50   $265.50  
  Purchase #4 $88.26   7.372%   $94.7665   $94.77   $94.75   $94.80  
  Purchase #5 $83.62   5.790%   $88.4616   $88.46   $88.45   $88.50  
  Purchase #6 $187.53   6.349%   $199.4363   $199.44   $199.45   $199.40  
  Purchase #7 $222.26   7.201%   $238.2649   $238.26   $238.25   $238.30  
  7 purchase totals = $964.39       $1,043.7026   $1,043.70   $1,043.65   $1,043.70