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 $149.34   9.123%   $162.9643   $162.96   $162.95   $163.00  
  Purchase #2 $180.76   13.677%   $205.4825   $205.48   $205.50   $205.50  
  Purchase #3 $75.49   12.482%   $84.9127   $84.91   $84.90   $84.90  
  Purchase #4 $164.69   3.245%   $170.0342   $170.03   $170.05   $170.00  
  Purchase #5 $67.46   13.204%   $76.3674   $76.37   $76.35   $76.40  
  Purchase #6 $61.31   5.375%   $64.6054   $64.61   $64.60   $64.60  
  Purchase #7 $192.52   12.521%   $216.6254   $216.63   $216.65   $216.60  
  7 purchase totals = $891.57       $980.9919   $980.99   $981.00   $981.00