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 $26.85   6.242%   $28.526   $28.53   $28.55   $28.50  
  Purchase #2 $91.26   5.737%   $96.4956   $96.50   $96.50   $96.50  
  Purchase #3 $171.85   11.738%   $192.0218   $192.02   $192.00   $192.00  
  Purchase #4 $178.91   12.589%   $201.433   $201.43   $201.45   $201.40  
  Purchase #5 $50.93   4.800%   $53.3746   $53.37   $53.35   $53.40  
  Purchase #6 $205.26   13.536%   $233.044   $233.04   $233.05   $233.00  
  Purchase #7 $18.39   8.315%   $19.9191   $19.92   $19.90   $19.90  
  7 purchase totals = $743.45       $824.8141   $824.81   $824.80   $824.70