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 $222.77   7.735%   $240.0013   $240.00   $240.00   $240.00  
  Purchase #2 $101.37   3.229%   $104.6432   $104.64   $104.65   $104.60  
  Purchase #3 $67.96   11.409%   $75.7136   $75.71   $75.70   $75.70  
  Purchase #4 $104.40   8.471%   $113.2437   $113.24   $113.25   $113.20  
  Purchase #5 $162.61   7.635%   $175.0253   $175.03   $175.05   $175.00  
  Purchase #6 $49.99   5.453%   $52.716   $52.72   $52.70   $52.70  
  Purchase #7 $164.70   3.731%   $170.845   $170.85   $170.85   $170.80  
  7 purchase totals = $873.80       $932.1881   $932.19   $932.20   $932.00