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 $110.83   4.268%   $115.5602   $115.56   $115.55   $115.60  
  Purchase #2 $185.28   11.164%   $205.9647   $205.96   $205.95   $206.00  
  Purchase #3 $126.74   4.643%   $132.6245   $132.62   $132.60   $132.60  
  Purchase #4 $57.70   10.688%   $63.867   $63.87   $63.85   $63.90  
  Purchase #5 $49.87   5.572%   $52.6488   $52.65   $52.65   $52.60  
  Purchase #6 $31.77   9.189%   $34.6893   $34.69   $34.70   $34.70  
  Purchase #7 $157.49   5.590%   $166.2937   $166.29   $166.30   $166.30  
  7 purchase totals = $719.68       $771.6482   $771.64   $771.60   $771.70