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 $125.29   13.273%   $141.9197   $141.92   $141.90   $141.90  
  Purchase #2 $111.93   5.392%   $117.9653   $117.97   $117.95   $118.00  
  Purchase #3 $53.38   10.293%   $58.8744   $58.87   $58.85   $58.90  
  Purchase #4 $93.60   11.723%   $104.5727   $104.57   $104.55   $104.60  
  Purchase #5 $193.86   13.751%   $220.5177   $220.52   $220.50   $220.50  
  Purchase #6 $111.87   12.744%   $126.1267   $126.13   $126.15   $126.10  
  Purchase #7 $59.33   13.519%   $67.3508   $67.35   $67.35   $67.40  
  7 purchase totals = $749.26       $837.3273   $837.33   $837.25   $837.40