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 $92.63   12.197%   $103.9281   $103.93   $103.95   $103.90  
  Purchase #2 $245.33   10.838%   $271.9189   $271.92   $271.90   $271.90  
  Purchase #3 $79.80   8.584%   $86.65   $86.65   $86.65   $86.70  
  Purchase #4 $38.56   6.745%   $41.1609   $41.16   $41.15   $41.20  
  Purchase #5 $195.33   10.274%   $215.3982   $215.40   $215.40   $215.40  
  Purchase #6 $178.74   5.565%   $188.6869   $188.69   $188.70   $188.70  
  Purchase #7 $132.72   6.279%   $141.0535   $141.05   $141.05   $141.10  
  7 purchase totals = $963.11       $1,048.7965   $1,048.80   $1,048.80   $1,048.90