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 $61.31   11.710%   $68.4894   $68.49   $68.50   $68.50  
  Purchase #2 $195.77   8.620%   $212.6454   $212.65   $212.65   $212.60  
  Purchase #3 $208.59   6.752%   $222.674   $222.67   $222.65   $222.70  
  Purchase #4 $69.79   3.764%   $72.4169   $72.42   $72.40   $72.40  
  Purchase #5 $180.36   12.449%   $202.813   $202.81   $202.80   $202.80  
  Purchase #6 $78.62   7.567%   $84.5692   $84.57   $84.55   $84.60  
  Purchase #7 $119.79   4.455%   $125.1266   $125.13   $125.15   $125.10  
  7 purchase totals = $914.23       $988.7345   $988.74   $988.70   $988.70