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 $61.47   7.851%   $66.296   $66.30   $66.30   $66.30  
  Purchase #2 $211.97   6.628%   $226.0194   $226.02   $226.00   $226.00  
  Purchase #3 $116.51   8.785%   $126.7454   $126.75   $126.75   $126.70  
  Purchase #4 $65.39   4.247%   $68.1671   $68.17   $68.15   $68.20  
  Purchase #5 $6.78   11.796%   $7.5798   $7.58   $7.60   $7.60  
  Purchase #6 $214.84   6.132%   $228.014   $228.01   $228.00   $228.00  
  Purchase #7 $90.71   11.257%   $100.9212   $100.92   $100.90   $100.90  
  7 purchase totals = $767.67       $823.7429   $823.75   $823.70   $823.70