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 $59.96   6.486%   $63.849   $63.85   $63.85   $63.80  
  Purchase #2 $81.32   8.546%   $88.2696   $88.27   $88.25   $88.30  
  Purchase #3 $218.60   11.707%   $244.1915   $244.19   $244.20   $244.20  
  Purchase #4 $125.34   8.162%   $135.5703   $135.57   $135.55   $135.60  
  Purchase #5 $59.25   10.452%   $65.4428   $65.44   $65.45   $65.40  
  Purchase #6 $142.87   4.442%   $149.2163   $149.22   $149.20   $149.20  
  Purchase #7 $208.94   8.564%   $226.8336   $226.83   $226.85   $226.80  
  7 purchase totals = $896.28       $973.3731   $973.37   $973.35   $973.30