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 $93.61   10.644%   $103.5738   $103.57   $103.55   $103.60  
  Purchase #2 $234.63   13.337%   $265.9226   $265.92   $265.90   $265.90  
  Purchase #3 $48.43   8.400%   $52.4981   $52.50   $52.50   $52.50  
  Purchase #4 $167.69   10.381%   $185.0979   $185.10   $185.10   $185.10  
  Purchase #5 $188.63   13.469%   $214.0366   $214.04   $214.05   $214.00  
  Purchase #6 $182.65   3.124%   $188.356   $188.36   $188.35   $188.40  
  Purchase #7 $46.80   9.481%   $51.2371   $51.24   $51.25   $51.20  
  7 purchase totals = $962.44       $1,060.7221   $1,060.73   $1,060.70   $1,060.70