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 $41.97   5.681%   $44.3543   $44.35   $44.35   $44.40  
  Purchase #2 $229.62   11.839%   $256.8047   $256.80   $256.80   $256.80  
  Purchase #3 $216.45   13.832%   $246.3894   $246.39   $246.40   $246.40  
  Purchase #4 $48.78   4.294%   $50.8746   $50.87   $50.85   $50.90  
  Purchase #5 $156.51   13.650%   $177.8736   $177.87   $177.85   $177.90  
  Purchase #6 $250.66   8.846%   $272.8334   $272.83   $272.85   $272.80  
  Purchase #7 $180.77   11.371%   $201.3254   $201.33   $201.35   $201.30  
  7 purchase totals = $1,124.76       $1,250.4554   $1,250.44   $1,250.45   $1,250.50