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 $22.72   6.131%   $24.113   $24.11   $24.10   $24.10  
  Purchase #2 $15.31   13.668%   $17.4026   $17.40   $17.40   $17.40  
  Purchase #3 $77.91   7.526%   $83.7735   $83.77   $83.75   $83.80  
  Purchase #4 $9.74   13.830%   $11.087   $11.09   $11.10   $11.10  
  Purchase #5 $208.91   12.593%   $235.218   $235.22   $235.20   $235.20  
  Purchase #6 $176.75   10.651%   $195.5756   $195.58   $195.60   $195.60  
  Purchase #7 $112.99   12.817%   $127.4719   $127.47   $127.45   $127.50  
  7 purchase totals = $624.33       $694.6416   $694.64   $694.60   $694.70