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 $93.61   6.499%   $99.6937   $99.69   $99.70   $99.70  
  Purchase #2 $162.60   13.563%   $184.6534   $184.65   $184.65   $184.70  
  Purchase #3 $76.59   6.722%   $81.7384   $81.74   $81.75   $81.70  
  Purchase #4 $107.38   11.469%   $119.6954   $119.70   $119.70   $119.70  
  Purchase #5 $229.99   4.179%   $239.6013   $239.60   $239.60   $239.60  
  Purchase #6 $131.94   4.200%   $137.4815   $137.48   $137.50   $137.50  
  Purchase #7 $31.90   6.455%   $33.9591   $33.96   $33.95   $34.00  
  7 purchase totals = $834.01       $896.8228   $896.82   $896.85   $896.90