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 $245.85   12.542%   $276.6845   $276.68   $276.70   $276.70  
  Purchase #2 $188.65   3.702%   $195.6338   $195.63   $195.65   $195.60  
  Purchase #3 $135.76   9.370%   $148.4807   $148.48   $148.50   $148.50  
  Purchase #4 $86.41   8.304%   $93.5855   $93.59   $93.60   $93.60  
  Purchase #5 $68.64   13.274%   $77.7513   $77.75   $77.75   $77.80  
  Purchase #6 $163.27   11.524%   $182.0852   $182.09   $182.10   $182.10  
  Purchase #7 $33.47   10.187%   $36.8796   $36.88   $36.90   $36.90  
  7 purchase totals = $922.05       $1,011.1006   $1,011.10   $1,011.20   $1,011.20