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 $87.44   12.505%   $98.3744   $98.37   $98.35   $98.40  
  Purchase #2 $222.58   5.723%   $235.3183   $235.32   $235.30   $235.30  
  Purchase #3 $73.41   11.667%   $81.9747   $81.97   $81.95   $82.00  
  Purchase #4 $167.65   8.601%   $182.0696   $182.07   $182.05   $182.10  
  Purchase #5 $230.62   8.359%   $249.8975   $249.90   $249.90   $249.90  
  Purchase #6 $83.39   12.661%   $93.948   $93.95   $93.95   $93.90  
  Purchase #7 $67.58   9.671%   $74.1157   $74.12   $74.10   $74.10  
  7 purchase totals = $932.67       $1,015.6982   $1,015.70   $1,015.60   $1,015.70