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 $214.83   3.217%   $221.7411   $221.74   $221.75   $221.70  
  Purchase #2 $244.71   6.558%   $260.7581   $260.76   $260.75   $260.80  
  Purchase #3 $173.82   11.544%   $193.8858   $193.89   $193.90   $193.90  
  Purchase #4 $106.26   10.510%   $117.4279   $117.43   $117.45   $117.40  
  Purchase #5 $222.42   11.210%   $247.3533   $247.35   $247.35   $247.40  
  Purchase #6 $233.89   6.672%   $249.4951   $249.50   $249.50   $249.50  
  Purchase #7 $8.99   5.731%   $9.5052   $9.51   $9.50   $9.50  
  7 purchase totals = $1,204.92       $1,300.1665   $1,300.18   $1,300.20   $1,300.20