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 $126.36   8.445%   $137.0311   $137.03   $137.05   $137.00  
  Purchase #2 $199.42   11.332%   $222.0183   $222.02   $222.00   $222.00  
  Purchase #3 $231.60   4.409%   $241.8112   $241.81   $241.80   $241.80  
  Purchase #4 $206.30   3.635%   $213.799   $213.80   $213.80   $213.80  
  Purchase #5 $46.26   12.833%   $52.1965   $52.20   $52.20   $52.20  
  Purchase #6 $57.85   4.513%   $60.4608   $60.46   $60.45   $60.50  
  Purchase #7 $92.32   7.134%   $98.9061   $98.91   $98.90   $98.90  
  7 purchase totals = $960.11       $1,026.2230   $1,026.23   $1,026.20   $1,026.20