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 $113.84   13.283%   $128.9614   $128.96   $128.95   $129.00  
  Purchase #2 $108.53   13.750%   $123.4529   $123.45   $123.45   $123.50  
  Purchase #3 $112.74   4.866%   $118.2259   $118.23   $118.25   $118.20  
  Purchase #4 $162.34   12.353%   $182.3939   $182.39   $182.40   $182.40  
  Purchase #5 $215.74   12.326%   $242.3321   $242.33   $242.35   $242.30  
  Purchase #6 $76.48   10.336%   $84.385   $84.39   $84.40   $84.40  
  Purchase #7 $127.63   13.774%   $145.2098   $145.21   $145.20   $145.20  
  7 purchase totals = $917.30       $1,024.9610   $1,024.96   $1,025.00   $1,025.00