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 $160.62   3.157%   $165.6908   $165.69   $165.70   $165.70  
  Purchase #2 $244.74   5.593%   $258.4283   $258.43   $258.45   $258.40  
  Purchase #3 $161.38   9.385%   $176.5255   $176.53   $176.55   $176.50  
  Purchase #4 $240.78   12.462%   $270.786   $270.79   $270.80   $270.80  
  Purchase #5 $38.39   6.713%   $40.9671   $40.97   $40.95   $41.00  
  Purchase #6 $46.87   10.754%   $51.9104   $51.91   $51.90   $51.90  
  Purchase #7 $96.25   11.141%   $106.9732   $106.97   $106.95   $107.00  
  7 purchase totals = $989.03       $1,071.2813   $1,071.29   $1,071.30   $1,071.30