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 $26.68   10.801%   $29.5617   $29.56   $29.55   $29.60  
  Purchase #2 $183.56   9.619%   $201.2166   $201.22   $201.20   $201.20  
  Purchase #3 $248.27   8.239%   $268.725   $268.73   $268.75   $268.70  
  Purchase #4 $74.74   11.803%   $83.5616   $83.56   $83.55   $83.60  
  Purchase #5 $196.63   10.378%   $217.0363   $217.04   $217.05   $217.00  
  Purchase #6 $120.95   8.102%   $130.7494   $130.75   $130.75   $130.70  
  Purchase #7 $105.99   8.627%   $115.1338   $115.13   $115.15   $115.10  
  7 purchase totals = $956.82       $1,045.9844   $1,045.99   $1,046.00   $1,045.90