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 $169.87   8.433%   $184.1951   $184.20   $184.20   $184.20  
  Purchase #2 $208.88   9.126%   $227.9424   $227.94   $227.95   $227.90  
  Purchase #3 $16.36   9.515%   $17.9167   $17.92   $17.90   $17.90  
  Purchase #4 $244.52   8.733%   $265.8739   $265.87   $265.85   $265.90  
  Purchase #5 $167.73   12.655%   $188.9562   $188.96   $188.95   $189.00  
  Purchase #6 $23.63   7.461%   $25.393   $25.39   $25.40   $25.40  
  Purchase #7 $182.30   3.164%   $188.068   $188.07   $188.05   $188.10  
  7 purchase totals = $1,013.29       $1,098.3453   $1,098.35   $1,098.30   $1,098.40