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 $61.54   8.346%   $66.6761   $66.68   $66.70   $66.70  
  Purchase #2 $165.91   12.142%   $186.0548   $186.05   $186.05   $186.10  
  Purchase #3 $124.79   12.278%   $140.1117   $140.11   $140.10   $140.10  
  Purchase #4 $23.50   3.281%   $24.271   $24.27   $24.25   $24.30  
  Purchase #5 $165.87   10.150%   $182.7058   $182.71   $182.70   $182.70  
  Purchase #6 $229.93   8.748%   $250.0443   $250.04   $250.05   $250.00  
  Purchase #7 $61.81   10.490%   $68.2939   $68.29   $68.30   $68.30  
  7 purchase totals = $833.35       $918.1576   $918.15   $918.15   $918.20