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 $226.57   8.250%   $245.262   $245.26   $245.25   $245.30  
  Purchase #2 $133.43   12.628%   $150.2795   $150.28   $150.30   $150.30  
  Purchase #3 $46.53   12.357%   $52.2797   $52.28   $52.30   $52.30  
  Purchase #4 $218.98   8.287%   $237.1269   $237.13   $237.15   $237.10  
  Purchase #5 $108.54   7.439%   $116.6143   $116.61   $116.60   $116.60  
  Purchase #6 $23.75   5.698%   $25.1033   $25.10   $25.10   $25.10  
  Purchase #7 $58.40   13.204%   $66.1111   $66.11   $66.10   $66.10  
  7 purchase totals = $816.20       $892.7768   $892.77   $892.80   $892.80