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 $188.51   12.547%   $212.1623   $212.16   $212.15   $212.20  
  Purchase #2 $25.71   3.824%   $26.6932   $26.69   $26.70   $26.70  
  Purchase #3 $15.49   13.833%   $17.6327   $17.63   $17.65   $17.60  
  Purchase #4 $40.85   9.472%   $44.7193   $44.72   $44.70   $44.70  
  Purchase #5 $242.78   4.117%   $252.7753   $252.78   $252.80   $252.80  
  Purchase #6 $236.49   3.533%   $244.8452   $244.85   $244.85   $244.80  
  Purchase #7 $216.47   7.279%   $232.2269   $232.23   $232.25   $232.20  
  7 purchase totals = $966.30       $1,031.0549   $1,031.06   $1,031.10   $1,031.00