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 $219.83   3.237%   $226.9459   $226.95   $226.95   $226.90  
  Purchase #2 $20.89   3.804%   $21.6847   $21.68   $21.70   $21.70  
  Purchase #3 $173.96   11.759%   $194.416   $194.42   $194.40   $194.40  
  Purchase #4 $30.55   11.257%   $33.989   $33.99   $34.00   $34.00  
  Purchase #5 $186.92   8.760%   $203.2942   $203.29   $203.30   $203.30  
  Purchase #6 $67.46   12.511%   $75.8999   $75.90   $75.90   $75.90  
  Purchase #7 $8.53   8.416%   $9.2479   $9.25   $9.25   $9.20  
  7 purchase totals = $708.14       $765.4776   $765.48   $765.50   $765.40