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 $144.93   9.584%   $158.8201   $158.82   $158.80   $158.80  
  Purchase #2 $68.27   11.815%   $76.3361   $76.34   $76.35   $76.30  
  Purchase #3 $217.71   4.806%   $228.1731   $228.17   $228.15   $228.20  
  Purchase #4 $47.39   10.173%   $52.211   $52.21   $52.20   $52.20  
  Purchase #5 $229.89   11.872%   $257.1825   $257.18   $257.20   $257.20  
  Purchase #6 $53.91   8.797%   $58.6525   $58.65   $58.65   $58.70  
  Purchase #7 $203.47   10.802%   $225.4488   $225.45   $225.45   $225.40  
  7 purchase totals = $965.57       $1,056.8241   $1,056.82   $1,056.80   $1,056.80