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 $156.60   12.593%   $176.3206   $176.32   $176.30   $176.30  
  Purchase #2 $68.25   4.231%   $71.1377   $71.14   $71.15   $71.10  
  Purchase #3 $133.70   10.138%   $147.2545   $147.25   $147.25   $147.30  
  Purchase #4 $227.39   6.252%   $241.6064   $241.61   $241.60   $241.60  
  Purchase #5 $241.38   5.416%   $254.4531   $254.45   $254.45   $254.50  
  Purchase #6 $39.96   4.831%   $41.8905   $41.89   $41.90   $41.90  
  Purchase #7 $15.62   13.547%   $17.736   $17.74   $17.75   $17.70  
  7 purchase totals = $882.90       $950.3988   $950.40   $950.40   $950.40