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 $108.53   9.671%   $119.0259   $119.03   $119.05   $119.00  
  Purchase #2 $188.65   7.259%   $202.3441   $202.34   $202.35   $202.30  
  Purchase #3 $204.25   4.821%   $214.0969   $214.10   $214.10   $214.10  
  Purchase #4 $26.92   4.751%   $28.199   $28.20   $28.20   $28.20  
  Purchase #5 $56.98   5.576%   $60.1572   $60.16   $60.15   $60.20  
  Purchase #6 $182.50   9.565%   $199.9561   $199.96   $199.95   $200.00  
  Purchase #7 $50.57   6.398%   $53.8055   $53.81   $53.80   $53.80  
  7 purchase totals = $818.40       $877.5847   $877.60   $877.60   $877.60