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 $191.42   12.420%   $215.1944   $215.19   $215.20   $215.20  
  Purchase #2 $45.58   11.167%   $50.6699   $50.67   $50.65   $50.70  
  Purchase #3 $201.53   4.334%   $210.2643   $210.26   $210.25   $210.30  
  Purchase #4 $95.42   11.744%   $106.6261   $106.63   $106.65   $106.60  
  Purchase #5 $73.77   4.285%   $76.931   $76.93   $76.95   $76.90  
  Purchase #6 $116.80   13.421%   $132.4757   $132.48   $132.50   $132.50  
  Purchase #7 $226.61   12.447%   $254.8161   $254.82   $254.80   $254.80  
  7 purchase totals = $951.13       $1,046.9775   $1,046.98   $1,047.00   $1,047.00