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 $58.51   12.523%   $65.8372   $65.84   $65.85   $65.80  
  Purchase #2 $97.49   9.389%   $106.6433   $106.64   $106.65   $106.60  
  Purchase #3 $133.43   10.466%   $147.3948   $147.39   $147.40   $147.40  
  Purchase #4 $26.29   9.768%   $28.858   $28.86   $28.85   $28.90  
  Purchase #5 $26.59   13.851%   $30.273   $30.27   $30.25   $30.30  
  Purchase #6 $194.54   12.821%   $219.482   $219.48   $219.50   $219.50  
  Purchase #7 $94.82   7.355%   $101.794   $101.79   $101.80   $101.80  
  7 purchase totals = $631.67       $700.2823   $700.27   $700.30   $700.30