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 $66.30   13.249%   $75.0841   $75.08   $75.10   $75.10  
  Purchase #2 $151.67   13.788%   $172.5823   $172.58   $172.60   $172.60  
  Purchase #3 $13.77   7.499%   $14.8026   $14.80   $14.80   $14.80  
  Purchase #4 $229.52   13.862%   $261.3361   $261.34   $261.35   $261.30  
  Purchase #5 $31.41   10.588%   $34.7357   $34.74   $34.75   $34.70  
  Purchase #6 $158.63   8.559%   $172.2071   $172.21   $172.20   $172.20  
  Purchase #7 $23.25   5.714%   $24.5785   $24.58   $24.60   $24.60  
  7 purchase totals = $674.55       $755.3264   $755.33   $755.40   $755.30