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 $72.45   6.671%   $77.2831   $77.28   $77.30   $77.30  
  Purchase #2 $215.43   5.665%   $227.6341   $227.63   $227.65   $227.60  
  Purchase #3 $154.57   6.592%   $164.7593   $164.76   $164.75   $164.80  
  Purchase #4 $54.89   10.331%   $60.5607   $60.56   $60.55   $60.60  
  Purchase #5 $197.98   6.292%   $210.4369   $210.44   $210.45   $210.40  
  Purchase #6 $99.92   13.303%   $113.2124   $113.21   $113.20   $113.20  
  Purchase #7 $170.56   13.340%   $193.3127   $193.31   $193.30   $193.30  
  7 purchase totals = $965.80       $1,047.1992   $1,047.19   $1,047.20   $1,047.20