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 $83.96   13.277%   $95.1074   $95.11   $95.10   $95.10  
  Purchase #2 $231.83   6.346%   $246.5419   $246.54   $246.55   $246.50  
  Purchase #3 $102.67   5.631%   $108.4513   $108.45   $108.45   $108.50  
  Purchase #4 $6.98   11.689%   $7.7959   $7.80   $7.80   $7.80  
  Purchase #5 $44.87   7.231%   $48.1145   $48.11   $48.10   $48.10  
  Purchase #6 $235.90   11.386%   $262.7596   $262.76   $262.75   $262.80  
  Purchase #7 $63.77   3.842%   $66.22   $66.22   $66.20   $66.20  
  7 purchase totals = $769.98       $834.9906   $834.99   $834.95   $835.00