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 $65.96   13.735%   $75.0196   $75.02   $75.00   $75.00  
  Purchase #2 $198.35   5.215%   $208.694   $208.69   $208.70   $208.70  
  Purchase #3 $95.32   7.487%   $102.4566   $102.46   $102.45   $102.50  
  Purchase #4 $79.37   7.693%   $85.4759   $85.48   $85.50   $85.50  
  Purchase #5 $94.35   3.367%   $97.5268   $97.53   $97.55   $97.50  
  Purchase #6 $97.50   6.182%   $103.5275   $103.53   $103.55   $103.50  
  Purchase #7 $215.46   3.164%   $222.2772   $222.28   $222.30   $222.30  
  7 purchase totals = $846.31       $894.9776   $894.99   $895.05   $895.00