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 $216.52   9.118%   $236.2623   $236.26   $236.25   $236.30  
  Purchase #2 $34.93   11.392%   $38.9092   $38.91   $38.90   $38.90  
  Purchase #3 $166.73   9.692%   $182.8895   $182.89   $182.90   $182.90  
  Purchase #4 $102.74   4.822%   $107.6941   $107.69   $107.70   $107.70  
  Purchase #5 $152.65   11.667%   $170.4597   $170.46   $170.45   $170.50  
  Purchase #6 $205.38   10.633%   $227.2181   $227.22   $227.20   $227.20  
  Purchase #7 $12.68   4.314%   $13.227   $13.23   $13.25   $13.20  
  7 purchase totals = $891.63       $976.6599   $976.66   $976.65   $976.70