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 $22.25   10.466%   $24.5787   $24.58   $24.60   $24.60  
  Purchase #2 $192.57   3.822%   $199.93   $199.93   $199.95   $199.90  
  Purchase #3 $118.87   3.134%   $122.5954   $122.60   $122.60   $122.60  
  Purchase #4 $112.66   5.383%   $118.7245   $118.72   $118.70   $118.70  
  Purchase #5 $149.62   4.574%   $156.4636   $156.46   $156.45   $156.50  
  Purchase #6 $160.75   8.141%   $173.8367   $173.84   $173.85   $173.80  
  Purchase #7 $193.38   12.194%   $216.9608   $216.96   $216.95   $217.00  
  7 purchase totals = $950.10       $1,013.0897   $1,013.09   $1,013.10   $1,013.10