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 $202.71   11.797%   $226.6237   $226.62   $226.60   $226.60  
  Purchase #2 $167.40   5.825%   $177.1511   $177.15   $177.15   $177.20  
  Purchase #3 $194.77   5.390%   $205.2681   $205.27   $205.25   $205.30  
  Purchase #4 $161.78   10.378%   $178.5695   $178.57   $178.55   $178.60  
  Purchase #5 $159.92   9.782%   $175.5634   $175.56   $175.55   $175.60  
  Purchase #6 $212.49   3.538%   $220.0079   $220.01   $220.00   $220.00  
  Purchase #7 $250.26   4.133%   $260.6032   $260.60   $260.60   $260.60  
  7 purchase totals = $1,349.33       $1,443.7869   $1,443.78   $1,443.70   $1,443.90