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 $177.65   13.427%   $201.5031   $201.50   $201.50   $201.50  
  Purchase #2 $238.94   7.151%   $256.0266   $256.03   $256.05   $256.00  
  Purchase #3 $94.67   8.564%   $102.7775   $102.78   $102.80   $102.80  
  Purchase #4 $60.68   9.380%   $66.3718   $66.37   $66.35   $66.40  
  Purchase #5 $209.51   7.829%   $225.9125   $225.91   $225.90   $225.90  
  Purchase #6 $55.44   5.595%   $58.5419   $58.54   $58.55   $58.50  
  Purchase #7 $57.32   3.198%   $59.1531   $59.15   $59.15   $59.20  
  7 purchase totals = $894.21       $970.2865   $970.28   $970.30   $970.30