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 $55.31   12.752%   $62.3631   $62.36   $62.35   $62.40  
  Purchase #2 $92.53   4.583%   $96.7706   $96.77   $96.75   $96.80  
  Purchase #3 $176.93   12.454%   $198.9649   $198.96   $198.95   $199.00  
  Purchase #4 $15.48   8.821%   $16.8455   $16.85   $16.85   $16.80  
  Purchase #5 $148.35   9.116%   $161.8736   $161.87   $161.85   $161.90  
  Purchase #6 $85.94   6.569%   $91.5854   $91.59   $91.60   $91.60  
  Purchase #7 $113.42   7.568%   $122.0036   $122.00   $122.00   $122.00  
  7 purchase totals = $687.96       $750.4067   $750.40   $750.35   $750.50