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 $87.84   9.432%   $96.1251   $96.13   $96.15   $96.10  
  Purchase #2 $196.60   6.730%   $209.8312   $209.83   $209.85   $209.80  
  Purchase #3 $95.55   8.812%   $103.9699   $103.97   $103.95   $104.00  
  Purchase #4 $216.54   6.779%   $231.2192   $231.22   $231.20   $231.20  
  Purchase #5 $237.69   3.383%   $245.7311   $245.73   $245.75   $245.70  
  Purchase #6 $125.81   7.483%   $135.2244   $135.22   $135.20   $135.20  
  Purchase #7 $76.60   13.591%   $87.0107   $87.01   $87.00   $87.00  
  7 purchase totals = $1,036.63       $1,109.1116   $1,109.11   $1,109.10   $1,109.00