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 $164.48   10.812%   $182.2636   $182.26   $182.25   $182.30  
  Purchase #2 $141.65   9.120%   $154.5685   $154.57   $154.55   $154.60  
  Purchase #3 $243.54   6.361%   $259.0316   $259.03   $259.05   $259.00  
  Purchase #4 $226.78   3.863%   $235.5405   $235.54   $235.55   $235.50  
  Purchase #5 $182.79   8.756%   $198.7951   $198.80   $198.80   $198.80  
  Purchase #6 $96.80   6.245%   $102.8452   $102.85   $102.85   $102.80  
  Purchase #7 $230.64   8.174%   $249.4925   $249.49   $249.50   $249.50  
  7 purchase totals = $1,286.68       $1,382.5370   $1,382.54   $1,382.55   $1,382.50