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 $224.39   9.146%   $244.9127   $244.91   $244.90   $244.90  
  Purchase #2 $130.91   3.839%   $135.9356   $135.94   $135.95   $135.90  
  Purchase #3 $208.79   11.741%   $233.304   $233.30   $233.30   $233.30  
  Purchase #4 $20.53   7.817%   $22.1348   $22.13   $22.15   $22.10  
  Purchase #5 $204.55   6.478%   $217.8007   $217.80   $217.80   $217.80  
  Purchase #6 $44.58   6.528%   $47.4902   $47.49   $47.50   $47.50  
  Purchase #7 $174.58   10.389%   $192.7171   $192.72   $192.70   $192.70  
  7 purchase totals = $1,008.33       $1,094.2951   $1,094.29   $1,094.30   $1,094.20