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 $166.85   10.628%   $184.5828   $184.58   $184.60   $184.60  
  Purchase #2 $200.28   11.221%   $222.7534   $222.75   $222.75   $222.80  
  Purchase #3 $151.66   10.216%   $167.1536   $167.15   $167.15   $167.20  
  Purchase #4 $235.59   6.114%   $249.994   $249.99   $250.00   $250.00  
  Purchase #5 $57.70   8.607%   $62.6662   $62.67   $62.65   $62.70  
  Purchase #6 $187.72   6.344%   $199.629   $199.63   $199.65   $199.60  
  Purchase #7 $67.58   13.818%   $76.9182   $76.92   $76.90   $76.90  
  7 purchase totals = $1,067.38       $1,163.6972   $1,163.69   $1,163.70   $1,163.80