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 $67.94   5.102%   $71.4063   $71.41   $71.40   $71.40  
  Purchase #2 $152.48   10.416%   $168.3623   $168.36   $168.35   $168.40  
  Purchase #3 $43.95   10.460%   $48.5472   $48.55   $48.55   $48.50  
  Purchase #4 $223.60   11.176%   $248.5895   $248.59   $248.60   $248.60  
  Purchase #5 $87.39   6.601%   $93.1586   $93.16   $93.15   $93.20  
  Purchase #6 $124.97   5.631%   $132.0071   $132.01   $132.00   $132.00  
  Purchase #7 $57.40   13.263%   $65.013   $65.01   $65.00   $65.00  
  7 purchase totals = $757.73       $827.0840   $827.09   $827.05   $827.10