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 $60.79   5.289%   $64.0052   $64.01   $64.00   $64.00  
  Purchase #2 $92.39   5.844%   $97.7893   $97.79   $97.80   $97.80  
  Purchase #3 $231.68   6.456%   $246.6373   $246.64   $246.65   $246.60  
  Purchase #4 $7.44   4.584%   $7.781   $7.78   $7.80   $7.80  
  Purchase #5 $240.92   13.458%   $273.343   $273.34   $273.35   $273.30  
  Purchase #6 $99.96   12.537%   $112.492   $112.49   $112.50   $112.50  
  Purchase #7 $45.66   3.648%   $47.3257   $47.33   $47.35   $47.30  
  7 purchase totals = $778.84       $849.3735   $849.38   $849.45   $849.30