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 $86.85   3.148%   $89.584   $89.58   $89.60   $89.60  
  Purchase #2 $92.45   11.575%   $103.1511   $103.15   $103.15   $103.20  
  Purchase #3 $151.68   11.596%   $169.2688   $169.27   $169.25   $169.30  
  Purchase #4 $24.75   5.410%   $26.089   $26.09   $26.10   $26.10  
  Purchase #5 $195.71   3.186%   $201.9453   $201.95   $201.95   $201.90  
  Purchase #6 $13.59   11.267%   $15.1212   $15.12   $15.10   $15.10  
  Purchase #7 $128.25   8.211%   $138.7806   $138.78   $138.80   $138.80  
  7 purchase totals = $693.28       $743.9400   $743.94   $743.95   $744.00