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 $198.95   12.218%   $223.2577   $223.26   $223.25   $223.30  
  Purchase #2 $92.52   9.804%   $101.5907   $101.59   $101.60   $101.60  
  Purchase #3 $43.96   10.530%   $48.589   $48.59   $48.60   $48.60  
  Purchase #4 $109.92   8.805%   $119.5985   $119.60   $119.60   $119.60  
  Purchase #5 $107.82   13.232%   $122.0867   $122.09   $122.10   $122.10  
  Purchase #6 $109.34   9.528%   $119.7579   $119.76   $119.75   $119.80  
  Purchase #7 $117.52   4.739%   $123.0893   $123.09   $123.10   $123.10  
  7 purchase totals = $780.03       $857.9698   $857.98   $858.00   $858.10