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 $98.25   13.473%   $111.4872   $111.49   $111.50   $111.50  
  Purchase #2 $148.64   4.129%   $154.7773   $154.78   $154.80   $154.80  
  Purchase #3 $209.50   4.133%   $218.1586   $218.16   $218.15   $218.20  
  Purchase #4 $221.74   13.766%   $252.2647   $252.26   $252.25   $252.30  
  Purchase #5 $161.30   11.522%   $179.885   $179.89   $179.90   $179.90  
  Purchase #6 $241.36   12.330%   $271.1197   $271.12   $271.10   $271.10  
  Purchase #7 $78.33   4.642%   $81.9661   $81.97   $81.95   $82.00  
  7 purchase totals = $1,159.12       $1,269.6586   $1,269.67   $1,269.65   $1,269.80