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 $59.25   11.726%   $66.1977   $66.20   $66.20   $66.20  
  Purchase #2 $226.36   11.481%   $252.3484   $252.35   $252.35   $252.30  
  Purchase #3 $38.26   7.544%   $41.1463   $41.15   $41.15   $41.10  
  Purchase #4 $146.54   7.714%   $157.8441   $157.84   $157.85   $157.80  
  Purchase #5 $105.81   6.704%   $112.9035   $112.90   $112.90   $112.90  
  Purchase #6 $142.32   12.868%   $160.6337   $160.63   $160.65   $160.60  
  Purchase #7 $151.32   12.870%   $170.7949   $170.79   $170.80   $170.80  
  7 purchase totals = $869.86       $961.8686   $961.86   $961.90   $961.70