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 $30.54   12.431%   $34.3364   $34.34   $34.35   $34.30  
  Purchase #2 $151.94   5.783%   $160.7267   $160.73   $160.75   $160.70  
  Purchase #3 $229.32   7.659%   $246.8836   $246.88   $246.90   $246.90  
  Purchase #4 $93.97   11.775%   $105.035   $105.04   $105.05   $105.00  
  Purchase #5 $119.40   5.317%   $125.7485   $125.75   $125.75   $125.70  
  Purchase #6 $234.67   3.539%   $242.975   $242.98   $243.00   $243.00  
  Purchase #7 $220.87   13.131%   $249.8724   $249.87   $249.85   $249.90  
  7 purchase totals = $1,080.71       $1,165.5776   $1,165.59   $1,165.65   $1,165.50