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 $183.36   7.454%   $197.0277   $197.03   $197.05   $197.00  
  Purchase #2 $81.66   8.670%   $88.7399   $88.74   $88.75   $88.70  
  Purchase #3 $14.25   12.272%   $15.9988   $16.00   $16.00   $16.00  
  Purchase #4 $169.29   4.435%   $176.798   $176.80   $176.80   $176.80  
  Purchase #5 $78.99   5.202%   $83.0991   $83.10   $83.10   $83.10  
  Purchase #6 $22.90   7.472%   $24.6111   $24.61   $24.60   $24.60  
  Purchase #7 $182.71   10.318%   $201.562   $201.56   $201.55   $201.60  
  7 purchase totals = $733.16       $787.8366   $787.84   $787.85   $787.80