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 $197.57   4.221%   $205.9094   $205.91   $205.90   $205.90  
  Purchase #2 $32.58   6.519%   $34.7039   $34.70   $34.70   $34.70  
  Purchase #3 $249.30   10.601%   $275.7283   $275.73   $275.75   $275.70  
  Purchase #4 $196.53   6.173%   $208.6618   $208.66   $208.65   $208.70  
  Purchase #5 $92.51   5.223%   $97.3418   $97.34   $97.35   $97.30  
  Purchase #6 $34.60   7.352%   $37.1438   $37.14   $37.15   $37.10  
  Purchase #7 $64.29   9.653%   $70.4959   $70.50   $70.50   $70.50  
  7 purchase totals = $867.38       $929.9849   $929.98   $930.00   $929.90