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 $92.78   12.728%   $104.589   $104.59   $104.60   $104.60  
  Purchase #2 $96.45   13.662%   $109.627   $109.63   $109.65   $109.60  
  Purchase #3 $103.95   10.615%   $114.9843   $114.98   $115.00   $115.00  
  Purchase #4 $171.49   10.150%   $188.8962   $188.90   $188.90   $188.90  
  Purchase #5 $245.28   12.511%   $275.967   $275.97   $275.95   $276.00  
  Purchase #6 $246.54   8.403%   $267.2568   $267.26   $267.25   $267.30  
  Purchase #7 $87.72   12.455%   $98.6455   $98.65   $98.65   $98.60  
  7 purchase totals = $1,044.21       $1,159.9658   $1,159.98   $1,160.00   $1,160.00