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 $61.41   10.676%   $67.9661   $67.97   $67.95   $68.00  
  Purchase #2 $152.58   7.659%   $164.2661   $164.27   $164.25   $164.30  
  Purchase #3 $57.85   10.218%   $63.7611   $63.76   $63.75   $63.80  
  Purchase #4 $24.42   10.329%   $26.9423   $26.94   $26.95   $26.90  
  Purchase #5 $60.71   4.270%   $63.3023   $63.30   $63.30   $63.30  
  Purchase #6 $188.81   11.113%   $209.7925   $209.79   $209.80   $209.80  
  Purchase #7 $220.69   6.547%   $235.1386   $235.14   $235.15   $235.10  
  7 purchase totals = $766.47       $831.1690   $831.17   $831.15   $831.20