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 $188.84   10.157%   $208.0205   $208.02   $208.00   $208.00  
  Purchase #2 $205.83   3.458%   $212.9476   $212.95   $212.95   $212.90  
  Purchase #3 $112.89   5.570%   $119.178   $119.18   $119.20   $119.20  
  Purchase #4 $237.54   11.128%   $263.9735   $263.97   $263.95   $264.00  
  Purchase #5 $189.74   5.558%   $200.2857   $200.29   $200.30   $200.30  
  Purchase #6 $209.34   4.551%   $218.8671   $218.87   $218.85   $218.90  
  Purchase #7 $153.98   9.342%   $168.3648   $168.36   $168.35   $168.40  
  7 purchase totals = $1,298.16       $1,391.6372   $1,391.64   $1,391.60   $1,391.70