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 $201.97   8.734%   $219.6101   $219.61   $219.60   $219.60  
  Purchase #2 $168.49   7.567%   $181.2396   $181.24   $181.25   $181.20  
  Purchase #3 $96.50   8.546%   $104.7469   $104.75   $104.75   $104.70  
  Purchase #4 $76.88   5.279%   $80.9385   $80.94   $80.95   $80.90  
  Purchase #5 $30.72   8.270%   $33.2605   $33.26   $33.25   $33.30  
  Purchase #6 $101.61   10.806%   $112.59   $112.59   $112.60   $112.60  
  Purchase #7 $118.70   11.722%   $132.614   $132.61   $132.60   $132.60  
  7 purchase totals = $794.87       $864.9996   $865.00   $865.00   $864.90