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 $187.47   8.249%   $202.9344   $202.93   $202.95   $202.90  
  Purchase #2 $12.91   6.428%   $13.7399   $13.74   $13.75   $13.70  
  Purchase #3 $177.92   13.654%   $202.2132   $202.21   $202.20   $202.20  
  Purchase #4 $161.45   13.295%   $182.9148   $182.91   $182.90   $182.90  
  Purchase #5 $56.92   4.496%   $59.4791   $59.48   $59.50   $59.50  
  Purchase #6 $208.90   7.787%   $225.167   $225.17   $225.15   $225.20  
  Purchase #7 $61.26   11.412%   $68.251   $68.25   $68.25   $68.30  
  7 purchase totals = $866.83       $954.6994   $954.69   $954.70   $954.70