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 $119.58   12.463%   $134.4833   $134.48   $134.50   $134.50  
  Purchase #2 $103.55   10.783%   $114.7158   $114.72   $114.70   $114.70  
  Purchase #3 $12.43   6.159%   $13.1956   $13.20   $13.20   $13.20  
  Purchase #4 $164.95   7.125%   $176.7027   $176.70   $176.70   $176.70  
  Purchase #5 $95.74   3.429%   $99.0229   $99.02   $99.00   $99.00  
  Purchase #6 $143.83   4.447%   $150.2261   $150.23   $150.25   $150.20  
  Purchase #7 $168.39   7.472%   $180.9721   $180.97   $180.95   $181.00  
  7 purchase totals = $808.47       $869.3185   $869.32   $869.30   $869.30