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 $212.27   6.245%   $225.5263   $225.53   $225.55   $225.50  
  Purchase #2 $40.56   9.145%   $44.2692   $44.27   $44.25   $44.30  
  Purchase #3 $117.76   12.264%   $132.2021   $132.20   $132.20   $132.20  
  Purchase #4 $87.76   3.557%   $90.8816   $90.88   $90.90   $90.90  
  Purchase #5 $140.47   8.156%   $151.9267   $151.93   $151.95   $151.90  
  Purchase #6 $206.92   12.550%   $232.8885   $232.89   $232.90   $232.90  
  Purchase #7 $155.84   12.471%   $175.2748   $175.27   $175.25   $175.30  
  7 purchase totals = $961.58       $1,052.9692   $1,052.97   $1,053.00   $1,053.00