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 $64.76   5.289%   $68.1852   $68.19   $68.20   $68.20  
  Purchase #2 $24.72   8.855%   $26.909   $26.91   $26.90   $26.90  
  Purchase #3 $64.36   4.854%   $67.484   $67.48   $67.50   $67.50  
  Purchase #4 $128.61   4.673%   $134.6199   $134.62   $134.60   $134.60  
  Purchase #5 $235.58   7.193%   $252.5253   $252.53   $252.55   $252.50  
  Purchase #6 $60.62   13.557%   $68.8383   $68.84   $68.85   $68.80  
  Purchase #7 $106.66   5.374%   $112.3919   $112.39   $112.40   $112.40  
  7 purchase totals = $685.31       $730.9536   $730.96   $731.00   $730.90