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 $49.95   12.578%   $56.2327   $56.23   $56.25   $56.20  
  Purchase #2 $166.76   13.277%   $188.9007   $188.90   $188.90   $188.90  
  Purchase #3 $125.76   4.309%   $131.179   $131.18   $131.20   $131.20  
  Purchase #4 $248.40   7.508%   $267.0499   $267.05   $267.05   $267.00  
  Purchase #5 $206.97   9.523%   $226.6798   $226.68   $226.70   $226.70  
  Purchase #6 $126.67   10.776%   $140.32   $140.32   $140.30   $140.30  
  Purchase #7 $97.45   7.155%   $104.4225   $104.42   $104.40   $104.40  
  7 purchase totals = $1,021.96       $1,114.7846   $1,114.78   $1,114.80   $1,114.70