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 $81.65   13.170%   $92.4033   $92.40   $92.40   $92.40  
  Purchase #2 $177.29   8.539%   $192.4288   $192.43   $192.45   $192.40  
  Purchase #3 $35.98   8.148%   $38.9117   $38.91   $38.90   $38.90  
  Purchase #4 $69.55   9.234%   $75.9722   $75.97   $75.95   $76.00  
  Purchase #5 $165.83   8.207%   $179.4397   $179.44   $179.45   $179.40  
  Purchase #6 $176.43   11.871%   $197.374   $197.37   $197.35   $197.40  
  Purchase #7 $134.75   4.209%   $140.4216   $140.42   $140.40   $140.40  
  7 purchase totals = $841.48       $916.9513   $916.94   $916.90   $916.90