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 $202.68   6.873%   $216.6102   $216.61   $216.60   $216.60  
  Purchase #2 $238.99   13.225%   $270.5964   $270.60   $270.60   $270.60  
  Purchase #3 $112.79   4.269%   $117.605   $117.61   $117.60   $117.60  
  Purchase #4 $169.64   4.766%   $177.725   $177.73   $177.75   $177.70  
  Purchase #5 $62.51   12.359%   $70.2356   $70.24   $70.25   $70.20  
  Purchase #6 $37.35   5.228%   $39.3027   $39.30   $39.30   $39.30  
  Purchase #7 $110.42   13.163%   $124.9546   $124.95   $124.95   $125.00  
  7 purchase totals = $934.38       $1,017.0295   $1,017.04   $1,017.05   $1,017.00