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 $223.74   4.454%   $233.7054   $233.71   $233.70   $233.70  
  Purchase #2 $97.82   11.589%   $109.1564   $109.16   $109.15   $109.20  
  Purchase #3 $148.49   6.249%   $157.7691   $157.77   $157.75   $157.80  
  Purchase #4 $56.65   3.402%   $58.5772   $58.58   $58.60   $58.60  
  Purchase #5 $88.29   11.289%   $98.2571   $98.26   $98.25   $98.30  
  Purchase #6 $208.53   7.624%   $224.4283   $224.43   $224.45   $224.40  
  Purchase #7 $162.75   9.737%   $178.597   $178.60   $178.60   $178.60  
  7 purchase totals = $986.27       $1,060.4905   $1,060.51   $1,060.50   $1,060.60