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 $22.87   7.759%   $24.6445   $24.64   $24.65   $24.60  
  Purchase #2 $183.86   8.725%   $199.9018   $199.90   $199.90   $199.90  
  Purchase #3 $28.70   10.548%   $31.7273   $31.73   $31.75   $31.70  
  Purchase #4 $145.96   8.290%   $158.0601   $158.06   $158.05   $158.10  
  Purchase #5 $67.62   13.537%   $76.7737   $76.77   $76.75   $76.80  
  Purchase #6 $173.30   8.251%   $187.599   $187.60   $187.60   $187.60  
  Purchase #7 $235.72   4.328%   $245.922   $245.92   $245.90   $245.90  
  7 purchase totals = $858.03       $924.6284   $924.62   $924.60   $924.60