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 $94.60   3.571%   $97.9782   $97.98   $98.00   $98.00  
  Purchase #2 $159.25   3.207%   $164.3571   $164.36   $164.35   $164.40  
  Purchase #3 $181.99   12.246%   $204.2765   $204.28   $204.30   $204.30  
  Purchase #4 $154.79   13.223%   $175.2579   $175.26   $175.25   $175.30  
  Purchase #5 $48.26   6.523%   $51.408   $51.41   $51.40   $51.40  
  Purchase #6 $75.44   10.407%   $83.291   $83.29   $83.30   $83.30  
  Purchase #7 $73.34   3.573%   $75.9604   $75.96   $75.95   $76.00  
  7 purchase totals = $787.67       $852.5291   $852.54   $852.55   $852.70