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 $48.30   8.763%   $52.5325   $52.53   $52.55   $52.50  
  Purchase #2 $191.82   6.109%   $203.5383   $203.54   $203.55   $203.50  
  Purchase #3 $125.58   3.273%   $129.6902   $129.69   $129.70   $129.70  
  Purchase #4 $193.67   3.361%   $200.1792   $200.18   $200.20   $200.20  
  Purchase #5 $51.80   12.764%   $58.4118   $58.41   $58.40   $58.40  
  Purchase #6 $33.94   5.833%   $35.9197   $35.92   $35.90   $35.90  
  Purchase #7 $246.87   13.224%   $279.5161   $279.52   $279.50   $279.50  
  7 purchase totals = $891.98       $959.7878   $959.79   $959.80   $959.70