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 $58.59   11.268%   $65.1919   $65.19   $65.20   $65.20  
  Purchase #2 $85.75   7.317%   $92.0243   $92.02   $92.00   $92.00  
  Purchase #3 $63.63   7.200%   $68.2114   $68.21   $68.20   $68.20  
  Purchase #4 $46.49   13.745%   $52.8801   $52.88   $52.90   $52.90  
  Purchase #5 $208.36   3.586%   $215.8318   $215.83   $215.85   $215.80  
  Purchase #6 $133.61   5.691%   $141.2137   $141.21   $141.20   $141.20  
  Purchase #7 $147.55   9.524%   $161.6027   $161.60   $161.60   $161.60  
  7 purchase totals = $743.98       $796.9559   $796.94   $796.95   $796.90