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 $117.93   7.618%   $126.9139   $126.91   $126.90   $126.90  
  Purchase #2 $75.95   11.862%   $84.9592   $84.96   $84.95   $85.00  
  Purchase #3 $194.34   4.829%   $203.7247   $203.72   $203.70   $203.70  
  Purchase #4 $57.49   3.158%   $59.3055   $59.31   $59.30   $59.30  
  Purchase #5 $159.27   6.427%   $169.5063   $169.51   $169.50   $169.50  
  Purchase #6 $16.28   12.564%   $18.3254   $18.33   $18.35   $18.30  
  Purchase #7 $193.53   9.811%   $212.5172   $212.52   $212.50   $212.50  
  7 purchase totals = $814.79       $875.2522   $875.26   $875.20   $875.20