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 $165.59   6.127%   $175.7357   $175.74   $175.75   $175.70  
  Purchase #2 $188.38   6.233%   $200.1217   $200.12   $200.10   $200.10  
  Purchase #3 $96.46   6.165%   $102.4068   $102.41   $102.40   $102.40  
  Purchase #4 $15.44   4.621%   $16.1535   $16.15   $16.15   $16.20  
  Purchase #5 $187.94   13.524%   $213.357   $213.36   $213.35   $213.40  
  Purchase #6 $175.65   3.162%   $181.2041   $181.20   $181.20   $181.20  
  Purchase #7 $146.95   13.339%   $166.5517   $166.55   $166.55   $166.60  
  7 purchase totals = $976.41       $1,055.5305   $1,055.53   $1,055.50   $1,055.60