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 $129.27   13.669%   $146.9399   $146.94   $146.95   $146.90  
  Purchase #2 $91.78   4.380%   $95.8   $95.80   $95.80   $95.80  
  Purchase #3 $137.99   12.237%   $154.8758   $154.88   $154.90   $154.90  
  Purchase #4 $63.72   12.190%   $71.4875   $71.49   $71.50   $71.50  
  Purchase #5 $197.60   8.523%   $214.4414   $214.44   $214.45   $214.40  
  Purchase #6 $198.90   8.513%   $215.8324   $215.83   $215.85   $215.80  
  Purchase #7 $156.48   11.243%   $174.073   $174.07   $174.05   $174.10  
  7 purchase totals = $975.74       $1,073.4500   $1,073.45   $1,073.50   $1,073.40