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 $174.73   13.624%   $198.5352   $198.54   $198.55   $198.50  
  Purchase #2 $62.28   10.816%   $69.0162   $69.02   $69.00   $69.00  
  Purchase #3 $124.72   11.373%   $138.9044   $138.90   $138.90   $138.90  
  Purchase #4 $56.59   10.579%   $62.5767   $62.58   $62.60   $62.60  
  Purchase #5 $15.71   4.505%   $16.4177   $16.42   $16.40   $16.40  
  Purchase #6 $51.97   8.335%   $56.3017   $56.30   $56.30   $56.30  
  Purchase #7 $149.58   5.807%   $158.2661   $158.27   $158.25   $158.30  
  7 purchase totals = $635.58       $700.0180   $700.03   $700.00   $700.00