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 $85.72   12.351%   $96.3073   $96.31   $96.30   $96.30  
  Purchase #2 $214.50   5.195%   $225.6433   $225.64   $225.65   $225.60  
  Purchase #3 $206.83   10.393%   $228.3258   $228.33   $228.35   $228.30  
  Purchase #4 $53.85   7.648%   $57.9684   $57.97   $57.95   $58.00  
  Purchase #5 $212.94   13.681%   $242.0723   $242.07   $242.05   $242.10  
  Purchase #6 $6.26   11.207%   $6.9616   $6.96   $6.95   $7.00  
  Purchase #7 $14.83   5.601%   $15.6606   $15.66   $15.65   $15.70  
  7 purchase totals = $794.93       $872.9393   $872.94   $872.90   $873.00