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 $229.66   13.628%   $260.9581   $260.96   $260.95   $261.00  
  Purchase #2 $144.47   4.102%   $150.3962   $150.40   $150.40   $150.40  
  Purchase #3 $232.80   13.548%   $264.3397   $264.34   $264.35   $264.30  
  Purchase #4 $45.26   8.427%   $49.0741   $49.07   $49.05   $49.10  
  Purchase #5 $245.99   6.490%   $261.9548   $261.95   $261.95   $262.00  
  Purchase #6 $206.72   11.405%   $230.2964   $230.30   $230.30   $230.30  
  Purchase #7 $153.33   5.442%   $161.6742   $161.67   $161.65   $161.70  
  7 purchase totals = $1,258.23       $1,378.6935   $1,378.69   $1,378.65   $1,378.80