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 $246.88   8.616%   $268.1512   $268.15   $268.15   $268.20  
  Purchase #2 $24.63   3.719%   $25.546   $25.55   $25.55   $25.50  
  Purchase #3 $217.54   9.695%   $238.6305   $238.63   $238.65   $238.60  
  Purchase #4 $54.46   12.635%   $61.341   $61.34   $61.35   $61.30  
  Purchase #5 $75.87   13.507%   $86.1178   $86.12   $86.10   $86.10  
  Purchase #6 $105.32   11.844%   $117.7941   $117.79   $117.80   $117.80  
  Purchase #7 $249.72   10.857%   $276.8321   $276.83   $276.85   $276.80  
  7 purchase totals = $974.42       $1,074.4127   $1,074.41   $1,074.45   $1,074.30