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 $54.28   10.554%   $60.0087   $60.01   $60.00   $60.00  
  Purchase #2 $94.90   13.788%   $107.9848   $107.98   $108.00   $108.00  
  Purchase #3 $137.36   7.299%   $147.3859   $147.39   $147.40   $147.40  
  Purchase #4 $94.92   7.471%   $102.0115   $102.01   $102.00   $102.00  
  Purchase #5 $249.63   8.447%   $270.7162   $270.72   $270.70   $270.70  
  Purchase #6 $244.52   3.793%   $253.7946   $253.79   $253.80   $253.80  
  Purchase #7 $89.45   5.779%   $94.6193   $94.62   $94.60   $94.60  
  7 purchase totals = $965.06       $1,036.5210   $1,036.52   $1,036.50   $1,036.50