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 $87.83   5.270%   $92.4586   $92.46   $92.45   $92.50  
  Purchase #2 $116.86   3.496%   $120.9454   $120.95   $120.95   $120.90  
  Purchase #3 $105.73   7.791%   $113.9674   $113.97   $113.95   $114.00  
  Purchase #4 $142.65   13.585%   $162.029   $162.03   $162.05   $162.00  
  Purchase #5 $55.74   5.357%   $58.726   $58.73   $58.75   $58.70  
  Purchase #6 $186.41   8.844%   $202.8961   $202.90   $202.90   $202.90  
  Purchase #7 $67.57   13.271%   $76.5372   $76.54   $76.55   $76.50  
  7 purchase totals = $762.79       $827.5597   $827.58   $827.60   $827.50