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 $110.94   13.584%   $126.0101   $126.01   $126.00   $126.00  
  Purchase #2 $52.99   9.567%   $58.0596   $58.06   $58.05   $58.10  
  Purchase #3 $142.78   9.458%   $156.2841   $156.28   $156.30   $156.30  
  Purchase #4 $221.96   8.534%   $240.9021   $240.90   $240.90   $240.90  
  Purchase #5 $120.86   12.630%   $136.1246   $136.12   $136.10   $136.10  
  Purchase #6 $208.41   8.866%   $226.8876   $226.89   $226.90   $226.90  
  Purchase #7 $20.60   13.392%   $23.3588   $23.36   $23.35   $23.40  
  7 purchase totals = $878.54       $967.6269   $967.62   $967.60   $967.70