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 $230.68   11.741%   $257.7641   $257.76   $257.75   $257.80  
  Purchase #2 $20.79   13.183%   $23.5307   $23.53   $23.55   $23.50  
  Purchase #3 $96.45   3.203%   $99.5393   $99.54   $99.55   $99.50  
  Purchase #4 $61.31   12.810%   $69.1638   $69.16   $69.15   $69.20  
  Purchase #5 $209.93   8.144%   $227.0267   $227.03   $227.05   $227.00  
  Purchase #6 $124.81   11.555%   $139.2318   $139.23   $139.25   $139.20  
  Purchase #7 $218.62   8.806%   $237.8717   $237.87   $237.85   $237.90  
  7 purchase totals = $962.59       $1,054.1281   $1,054.12   $1,054.15   $1,054.10