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 $235.90   10.560%   $260.811   $260.81   $260.80   $260.80  
  Purchase #2 $250.76   3.271%   $258.9624   $258.96   $258.95   $259.00  
  Purchase #3 $70.33   9.741%   $77.1808   $77.18   $77.20   $77.20  
  Purchase #4 $241.89   7.160%   $259.2093   $259.21   $259.20   $259.20  
  Purchase #5 $238.69   5.821%   $252.5841   $252.58   $252.60   $252.60  
  Purchase #6 $250.61   5.187%   $263.6091   $263.61   $263.60   $263.60  
  Purchase #7 $240.77   4.135%   $250.7258   $250.73   $250.75   $250.70  
  7 purchase totals = $1,528.95       $1,623.0825   $1,623.08   $1,623.10   $1,623.10