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 $119.80   9.806%   $131.5476   $131.55   $131.55   $131.50  
  Purchase #2 $192.36   12.498%   $216.4012   $216.40   $216.40   $216.40  
  Purchase #3 $22.48   9.859%   $24.6963   $24.70   $24.70   $24.70  
  Purchase #4 $208.36   9.404%   $227.9542   $227.95   $227.95   $228.00  
  Purchase #5 $213.35   8.437%   $231.3503   $231.35   $231.35   $231.40  
  Purchase #6 $99.74   11.488%   $111.1981   $111.20   $111.20   $111.20  
  Purchase #7 $57.89   5.737%   $61.2111   $61.21   $61.20   $61.20  
  7 purchase totals = $913.98       $1,004.3588   $1,004.36   $1,004.35   $1,004.40