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 $218.60   6.766%   $233.3905   $233.39   $233.40   $233.40  
  Purchase #2 $197.53   4.302%   $206.0277   $206.03   $206.05   $206.00  
  Purchase #3 $250.80   5.401%   $264.3457   $264.35   $264.35   $264.30  
  Purchase #4 $147.49   9.332%   $161.2538   $161.25   $161.25   $161.30  
  Purchase #5 $203.73   11.345%   $226.8432   $226.84   $226.85   $226.80  
  Purchase #6 $96.26   4.259%   $100.3597   $100.36   $100.35   $100.40  
  Purchase #7 $48.40   10.816%   $53.6349   $53.63   $53.65   $53.60  
  7 purchase totals = $1,162.81       $1,245.8555   $1,245.85   $1,245.90   $1,245.80