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 $55.29   11.444%   $61.6174   $61.62   $61.60   $61.60  
  Purchase #2 $157.31   7.726%   $169.4638   $169.46   $169.45   $169.50  
  Purchase #3 $233.80   3.517%   $242.0227   $242.02   $242.00   $242.00  
  Purchase #4 $99.60   13.729%   $113.2741   $113.27   $113.25   $113.30  
  Purchase #5 $117.96   4.275%   $123.0028   $123.00   $123.00   $123.00  
  Purchase #6 $188.50   3.810%   $195.6819   $195.68   $195.70   $195.70  
  Purchase #7 $35.92   9.717%   $39.4103   $39.41   $39.40   $39.40  
  7 purchase totals = $888.38       $944.4730   $944.46   $944.40   $944.50