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 $211.92   10.576%   $234.3327   $234.33   $234.35   $234.30  
  Purchase #2 $138.58   3.680%   $143.6797   $143.68   $143.70   $143.70  
  Purchase #3 $25.38   4.702%   $26.5734   $26.57   $26.55   $26.60  
  Purchase #4 $121.39   9.104%   $132.4413   $132.44   $132.45   $132.40  
  Purchase #5 $136.55   5.311%   $143.8022   $143.80   $143.80   $143.80  
  Purchase #6 $67.87   13.320%   $76.9103   $76.91   $76.90   $76.90  
  Purchase #7 $201.50   3.534%   $208.621   $208.62   $208.60   $208.60  
  7 purchase totals = $903.19       $966.3606   $966.35   $966.35   $966.30