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 $150.26   13.844%   $171.062   $171.06   $171.05   $171.10  
  Purchase #2 $190.80   10.575%   $210.9771   $210.98   $211.00   $211.00  
  Purchase #3 $117.85   6.555%   $125.5751   $125.58   $125.60   $125.60  
  Purchase #4 $85.64   13.559%   $97.2519   $97.25   $97.25   $97.30  
  Purchase #5 $127.64   13.264%   $144.5702   $144.57   $144.55   $144.60  
  Purchase #6 $226.52   8.297%   $245.3144   $245.31   $245.30   $245.30  
  Purchase #7 $240.91   8.643%   $261.7319   $261.73   $261.75   $261.70  
  7 purchase totals = $1,139.62       $1,256.4826   $1,256.48   $1,256.50   $1,256.60