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 $224.41   9.213%   $245.0849   $245.08   $245.10   $245.10  
  Purchase #2 $76.72   13.198%   $86.8455   $86.85   $86.85   $86.80  
  Purchase #3 $151.84   10.475%   $167.7452   $167.75   $167.75   $167.70  
  Purchase #4 $59.75   8.593%   $64.8843   $64.88   $64.90   $64.90  
  Purchase #5 $177.85   10.836%   $197.1218   $197.12   $197.10   $197.10  
  Purchase #6 $169.67   10.844%   $188.069   $188.07   $188.05   $188.10  
  Purchase #7 $10.54   11.211%   $11.7216   $11.72   $11.70   $11.70  
  7 purchase totals = $870.78       $961.4723   $961.47   $961.45   $961.40