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 $58.47   11.217%   $65.0286   $65.03   $65.05   $65.00  
  Purchase #2 $89.41   7.485%   $96.1023   $96.10   $96.10   $96.10  
  Purchase #3 $138.73   7.567%   $149.2277   $149.23   $149.25   $149.20  
  Purchase #4 $184.98   12.630%   $208.343   $208.34   $208.35   $208.30  
  Purchase #5 $8.77   3.800%   $9.1033   $9.10   $9.10   $9.10  
  Purchase #6 $127.45   4.723%   $133.4695   $133.47   $133.45   $133.50  
  Purchase #7 $121.64   9.162%   $132.7847   $132.78   $132.80   $132.80  
  7 purchase totals = $729.45       $794.0591   $794.05   $794.10   $794.00