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 $94.86   3.226%   $97.9202   $97.92   $97.90   $97.90  
  Purchase #2 $178.27   8.238%   $192.9559   $192.96   $192.95   $193.00  
  Purchase #3 $127.26   8.519%   $138.1013   $138.10   $138.10   $138.10  
  Purchase #4 $14.96   7.410%   $16.0685   $16.07   $16.05   $16.10  
  Purchase #5 $23.88   9.399%   $26.1245   $26.12   $26.10   $26.10  
  Purchase #6 $20.73   13.512%   $23.531   $23.53   $23.55   $23.50  
  Purchase #7 $186.42   10.142%   $205.3267   $205.33   $205.35   $205.30  
  7 purchase totals = $646.38       $700.0281   $700.03   $700.00   $700.00