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 $232.57   10.271%   $256.4573   $256.46   $256.45   $256.50  
  Purchase #2 $224.77   4.471%   $234.8195   $234.82   $234.80   $234.80  
  Purchase #3 $205.70   6.436%   $218.9389   $218.94   $218.95   $218.90  
  Purchase #4 $131.28   3.235%   $135.5269   $135.53   $135.55   $135.50  
  Purchase #5 $198.40   3.749%   $205.838   $205.84   $205.85   $205.80  
  Purchase #6 $193.50   6.561%   $206.1955   $206.20   $206.20   $206.20  
  Purchase #7 $63.25   5.130%   $66.4947   $66.49   $66.50   $66.50  
  7 purchase totals = $1,249.47       $1,324.2708   $1,324.28   $1,324.30   $1,324.20