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 $23.96   10.781%   $26.5431   $26.54   $26.55   $26.50  
  Purchase #2 $79.75   4.769%   $83.5533   $83.55   $83.55   $83.60  
  Purchase #3 $157.27   12.699%   $177.2417   $177.24   $177.25   $177.20  
  Purchase #4 $248.72   6.190%   $264.1158   $264.12   $264.10   $264.10  
  Purchase #5 $52.55   10.178%   $57.8985   $57.90   $57.90   $57.90  
  Purchase #6 $202.39   4.289%   $211.0705   $211.07   $211.05   $211.10  
  Purchase #7 $139.53   8.225%   $151.0063   $151.01   $151.00   $151.00  
  7 purchase totals = $904.17       $971.4292   $971.43   $971.40   $971.40