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 $44.91   3.412%   $46.4423   $46.44   $46.45   $46.40  
  Purchase #2 $167.65   13.237%   $189.8418   $189.84   $189.85   $189.80  
  Purchase #3 $123.44   8.300%   $133.6855   $133.69   $133.70   $133.70  
  Purchase #4 $97.59   9.235%   $106.6024   $106.60   $106.60   $106.60  
  Purchase #5 $169.28   8.654%   $183.9295   $183.93   $183.95   $183.90  
  Purchase #6 $144.90   7.262%   $155.4226   $155.42   $155.40   $155.40  
  Purchase #7 $8.46   11.296%   $9.4156   $9.42   $9.40   $9.40  
  7 purchase totals = $756.23       $825.3397   $825.34   $825.35   $825.20