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 $243.47   6.445%   $259.1616   $259.16   $259.15   $259.20  
  Purchase #2 $182.76   11.749%   $204.2325   $204.23   $204.25   $204.20  
  Purchase #3 $23.93   5.261%   $25.189   $25.19   $25.20   $25.20  
  Purchase #4 $150.55   13.458%   $170.811   $170.81   $170.80   $170.80  
  Purchase #5 $225.74   8.831%   $245.6751   $245.68   $245.70   $245.70  
  Purchase #6 $153.43   4.801%   $160.7962   $160.80   $160.80   $160.80  
  Purchase #7 $234.61   12.359%   $263.6054   $263.61   $263.60   $263.60  
  7 purchase totals = $1,214.49       $1,329.4708   $1,329.48   $1,329.50   $1,329.50