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 $207.58   3.663%   $215.1837   $215.18   $215.20   $215.20  
  Purchase #2 $234.44   4.788%   $245.665   $245.67   $245.65   $245.70  
  Purchase #3 $26.84   5.833%   $28.4056   $28.41   $28.40   $28.40  
  Purchase #4 $173.63   12.158%   $194.7399   $194.74   $194.75   $194.70  
  Purchase #5 $74.83   11.248%   $83.2469   $83.25   $83.25   $83.20  
  Purchase #6 $232.92   8.168%   $251.9449   $251.94   $251.95   $251.90  
  Purchase #7 $66.57   8.122%   $71.9768   $71.98   $72.00   $72.00  
  7 purchase totals = $1,016.81       $1,091.1628   $1,091.17   $1,091.20   $1,091.10