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 $194.60   8.433%   $211.0106   $211.01   $211.00   $211.00  
  Purchase #2 $208.37   4.257%   $217.2403   $217.24   $217.25   $217.20  
  Purchase #3 $111.89   9.269%   $122.2611   $122.26   $122.25   $122.30  
  Purchase #4 $34.31   5.135%   $36.0718   $36.07   $36.05   $36.10  
  Purchase #5 $66.48   10.610%   $73.5335   $73.53   $73.55   $73.50  
  Purchase #6 $158.41   3.867%   $164.5357   $164.54   $164.55   $164.50  
  Purchase #7 $5.69   9.311%   $6.2198   $6.22   $6.20   $6.20  
  7 purchase totals = $779.75       $830.8728   $830.87   $830.85   $830.80