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 $177.48   10.212%   $195.6043   $195.60   $195.60   $195.60  
  Purchase #2 $68.84   8.499%   $74.6907   $74.69   $74.70   $74.70  
  Purchase #3 $115.46   13.129%   $130.6187   $130.62   $130.60   $130.60  
  Purchase #4 $211.55   4.268%   $220.579   $220.58   $220.60   $220.60  
  Purchase #5 $167.61   5.551%   $176.914   $176.91   $176.90   $176.90  
  Purchase #6 $5.74   7.486%   $6.1697   $6.17   $6.15   $6.20  
  Purchase #7 $47.67   10.835%   $52.835   $52.84   $52.85   $52.80  
  7 purchase totals = $794.35       $857.4114   $857.41   $857.40   $857.40