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 $72.73   12.422%   $81.7645   $81.76   $81.75   $81.80  
  Purchase #2 $102.53   10.246%   $113.0352   $113.04   $113.05   $113.00  
  Purchase #3 $112.45   6.169%   $119.387   $119.39   $119.40   $119.40  
  Purchase #4 $194.25   10.688%   $215.0114   $215.01   $215.00   $215.00  
  Purchase #5 $234.30   13.493%   $265.9141   $265.91   $265.90   $265.90  
  Purchase #6 $222.65   5.685%   $235.3077   $235.31   $235.30   $235.30  
  Purchase #7 $129.34   12.571%   $145.5993   $145.60   $145.60   $145.60  
  7 purchase totals = $1,068.25       $1,176.0192   $1,176.02   $1,176.00   $1,176.00