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 $65.77   11.126%   $73.0876   $73.09   $73.10   $73.10  
  Purchase #2 $175.55   4.781%   $183.943   $183.94   $183.95   $183.90  
  Purchase #3 $68.94   8.274%   $74.6441   $74.64   $74.65   $74.60  
  Purchase #4 $109.86   6.417%   $116.9097   $116.91   $116.90   $116.90  
  Purchase #5 $5.45   11.284%   $6.065   $6.07   $6.05   $6.10  
  Purchase #6 $230.49   3.725%   $239.0758   $239.08   $239.10   $239.10  
  Purchase #7 $148.66   11.647%   $165.9744   $165.97   $165.95   $166.00  
  7 purchase totals = $804.72       $859.6996   $859.70   $859.70   $859.70