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 $195.43   5.773%   $206.7122   $206.71   $206.70   $206.70  
  Purchase #2 $64.35   11.475%   $71.7342   $71.73   $71.75   $71.70  
  Purchase #3 $57.76   9.717%   $63.3725   $63.37   $63.35   $63.40  
  Purchase #4 $58.37   3.561%   $60.4486   $60.45   $60.45   $60.40  
  Purchase #5 $23.83   6.520%   $25.3837   $25.38   $25.40   $25.40  
  Purchase #6 $147.83   3.447%   $152.9257   $152.93   $152.95   $152.90  
  Purchase #7 $218.46   3.495%   $226.0952   $226.10   $226.10   $226.10  
  7 purchase totals = $766.03       $806.6721   $806.67   $806.70   $806.60