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 $206.86   11.687%   $231.0357   $231.04   $231.05   $231.00  
  Purchase #2 $132.54   7.109%   $141.9623   $141.96   $141.95   $142.00  
  Purchase #3 $236.31   13.535%   $268.2946   $268.29   $268.30   $268.30  
  Purchase #4 $70.37   13.504%   $79.8728   $79.87   $79.85   $79.90  
  Purchase #5 $215.33   11.384%   $239.8432   $239.84   $239.85   $239.80  
  Purchase #6 $61.36   5.464%   $64.7127   $64.71   $64.70   $64.70  
  Purchase #7 $132.25   9.706%   $145.0862   $145.09   $145.10   $145.10  
  7 purchase totals = $1,055.02       $1,170.8075   $1,170.80   $1,170.80   $1,170.80