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 $119.72   11.108%   $133.0185   $133.02   $133.00   $133.00  
  Purchase #2 $61.71   4.477%   $64.4728   $64.47   $64.45   $64.50  
  Purchase #3 $6.35   4.152%   $6.6137   $6.61   $6.60   $6.60  
  Purchase #4 $163.94   10.535%   $181.2111   $181.21   $181.20   $181.20  
  Purchase #5 $85.79   8.564%   $93.1371   $93.14   $93.15   $93.10  
  Purchase #6 $211.70   9.160%   $231.0917   $231.09   $231.10   $231.10  
  Purchase #7 $113.26   3.543%   $117.2728   $117.27   $117.25   $117.30  
  7 purchase totals = $762.47       $826.8177   $826.81   $826.75   $826.80