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 $234.96   12.744%   $264.9033   $264.90   $264.90   $264.90  
  Purchase #2 $20.31   13.543%   $23.0606   $23.06   $23.05   $23.10  
  Purchase #3 $151.48   8.597%   $164.5027   $164.50   $164.50   $164.50  
  Purchase #4 $239.74   5.605%   $253.1774   $253.18   $253.20   $253.20  
  Purchase #5 $225.60   8.717%   $245.2656   $245.27   $245.25   $245.30  
  Purchase #6 $155.54   6.726%   $166.0016   $166.00   $166.00   $166.00  
  Purchase #7 $43.50   5.829%   $46.0356   $46.04   $46.05   $46.00  
  7 purchase totals = $1,071.13       $1,162.9468   $1,162.95   $1,162.95   $1,163.00