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 $62.68   11.609%   $69.9565   $69.96   $69.95   $70.00  
  Purchase #2 $153.98   5.710%   $162.7723   $162.77   $162.75   $162.80  
  Purchase #3 $112.51   12.110%   $126.135   $126.14   $126.15   $126.10  
  Purchase #4 $36.73   7.272%   $39.401   $39.40   $39.40   $39.40  
  Purchase #5 $178.42   13.570%   $202.6316   $202.63   $202.65   $202.60  
  Purchase #6 $140.96   12.172%   $158.1177   $158.12   $158.10   $158.10  
  Purchase #7 $185.47   9.417%   $202.9357   $202.94   $202.95   $202.90  
  7 purchase totals = $870.75       $961.9498   $961.96   $961.95   $961.90