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 $96.95   10.557%   $107.185   $107.19   $107.20   $107.20  
  Purchase #2 $66.72   7.712%   $71.8654   $71.87   $71.85   $71.90  
  Purchase #3 $49.86   4.827%   $52.2667   $52.27   $52.25   $52.30  
  Purchase #4 $142.88   5.517%   $150.7627   $150.76   $150.75   $150.80  
  Purchase #5 $232.40   13.359%   $263.4463   $263.45   $263.45   $263.40  
  Purchase #6 $58.63   10.330%   $64.6865   $64.69   $64.70   $64.70  
  Purchase #7 $84.94   7.619%   $91.4116   $91.41   $91.40   $91.40  
  7 purchase totals = $732.38       $801.6242   $801.64   $801.60   $801.70