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 $200.63   6.678%   $214.0281   $214.03   $214.05   $214.00  
  Purchase #2 $125.50   4.872%   $131.6144   $131.61   $131.60   $131.60  
  Purchase #3 $206.42   8.415%   $223.7902   $223.79   $223.80   $223.80  
  Purchase #4 $91.84   6.252%   $97.5818   $97.58   $97.60   $97.60  
  Purchase #5 $55.34   4.549%   $57.8574   $57.86   $57.85   $57.90  
  Purchase #6 $14.64   12.432%   $16.46   $16.46   $16.45   $16.50  
  Purchase #7 $99.84   11.450%   $111.2717   $111.27   $111.25   $111.30  
  7 purchase totals = $794.21       $852.6036   $852.60   $852.60   $852.70