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 $55.73   13.573%   $63.2942   $63.29   $63.30   $63.30  
  Purchase #2 $96.81   8.793%   $105.3225   $105.32   $105.30   $105.30  
  Purchase #3 $211.75   8.286%   $229.2956   $229.30   $229.30   $229.30  
  Purchase #4 $117.40   11.214%   $130.5652   $130.57   $130.55   $130.60  
  Purchase #5 $80.46   8.180%   $87.0416   $87.04   $87.05   $87.00  
  Purchase #6 $44.68   6.389%   $47.5346   $47.53   $47.55   $47.50  
  Purchase #7 $99.74   5.616%   $105.3414   $105.34   $105.35   $105.30  
  7 purchase totals = $706.57       $768.3951   $768.39   $768.40   $768.30