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 $93.92   10.398%   $103.6858   $103.69   $103.70   $103.70  
  Purchase #2 $162.40   7.565%   $174.6856   $174.69   $174.70   $174.70  
  Purchase #3 $119.38   10.210%   $131.5687   $131.57   $131.55   $131.60  
  Purchase #4 $97.88   6.467%   $104.2099   $104.21   $104.20   $104.20  
  Purchase #5 $121.74   9.588%   $133.4124   $133.41   $133.40   $133.40  
  Purchase #6 $192.50   3.836%   $199.8843   $199.88   $199.90   $199.90  
  Purchase #7 $23.98   8.832%   $26.0979   $26.10   $26.10   $26.10  
  7 purchase totals = $811.80       $873.5446   $873.55   $873.55   $873.60