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 $240.59   9.808%   $264.1871   $264.19   $264.20   $264.20  
  Purchase #2 $22.49   12.591%   $25.3217   $25.32   $25.30   $25.30  
  Purchase #3 $56.34   9.139%   $61.4889   $61.49   $61.50   $61.50  
  Purchase #4 $249.59   9.802%   $274.0548   $274.05   $274.05   $274.10  
  Purchase #5 $53.29   3.663%   $55.242   $55.24   $55.25   $55.20  
  Purchase #6 $183.36   13.190%   $207.5452   $207.55   $207.55   $207.50  
  Purchase #7 $149.63   7.646%   $161.0707   $161.07   $161.05   $161.10  
  7 purchase totals = $955.29       $1,048.9104   $1,048.91   $1,048.90   $1,048.90