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 $49.84   9.417%   $54.5334   $54.53   $54.55   $54.50  
  Purchase #2 $157.76   10.744%   $174.7097   $174.71   $174.70   $174.70  
  Purchase #3 $198.29   4.651%   $207.5125   $207.51   $207.50   $207.50  
  Purchase #4 $157.36   10.846%   $174.4273   $174.43   $174.45   $174.40  
  Purchase #5 $19.70   13.571%   $22.3735   $22.37   $22.35   $22.40  
  Purchase #6 $41.99   6.218%   $44.6009   $44.60   $44.60   $44.60  
  Purchase #7 $236.65   8.170%   $255.9843   $255.98   $256.00   $256.00  
  7 purchase totals = $861.59       $934.1416   $934.13   $934.15   $934.10