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 $199.48   3.779%   $207.0183   $207.02   $207.00   $207.00  
  Purchase #2 $43.71   5.776%   $46.2347   $46.23   $46.25   $46.20  
  Purchase #3 $130.66   5.589%   $137.9626   $137.96   $137.95   $138.00  
  Purchase #4 $244.81   8.767%   $266.2725   $266.27   $266.25   $266.30  
  Purchase #5 $215.88   13.103%   $244.1668   $244.17   $244.15   $244.20  
  Purchase #6 $200.40   4.386%   $209.1895   $209.19   $209.20   $209.20  
  Purchase #7 $57.52   11.755%   $64.2815   $64.28   $64.30   $64.30  
  7 purchase totals = $1,092.46       $1,175.1259   $1,175.12   $1,175.10   $1,175.20