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 $84.34   11.334%   $93.8991   $93.90   $93.90   $93.90  
  Purchase #2 $189.87   6.714%   $202.6179   $202.62   $202.60   $202.60  
  Purchase #3 $67.91   9.760%   $74.538   $74.54   $74.55   $74.50  
  Purchase #4 $43.85   8.427%   $47.5452   $47.55   $47.55   $47.50  
  Purchase #5 $23.66   10.457%   $26.1341   $26.13   $26.15   $26.10  
  Purchase #6 $188.71   6.233%   $200.4723   $200.47   $200.45   $200.50  
  Purchase #7 $157.25   12.508%   $176.9188   $176.92   $176.90   $176.90  
  7 purchase totals = $755.59       $822.1254   $822.13   $822.10   $822.00