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 $55.63   7.766%   $59.9502   $59.95   $59.95   $60.00  
  Purchase #2 $32.26   7.310%   $34.6182   $34.62   $34.60   $34.60  
  Purchase #3 $133.70   5.685%   $141.3008   $141.30   $141.30   $141.30  
  Purchase #4 $112.74   10.338%   $124.3951   $124.40   $124.40   $124.40  
  Purchase #5 $193.89   7.168%   $207.788   $207.79   $207.80   $207.80  
  Purchase #6 $97.99   5.257%   $103.1413   $103.14   $103.15   $103.10  
  Purchase #7 $24.84   9.848%   $27.2862   $27.29   $27.30   $27.30  
  7 purchase totals = $651.05       $698.4798   $698.49   $698.50   $698.50