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 $213.34   12.592%   $240.2038   $240.20   $240.20   $240.20  
  Purchase #2 $51.81   3.822%   $53.7902   $53.79   $53.80   $53.80  
  Purchase #3 $156.98   12.691%   $176.9023   $176.90   $176.90   $176.90  
  Purchase #4 $108.84   5.855%   $115.2126   $115.21   $115.20   $115.20  
  Purchase #5 $190.82   11.116%   $212.0316   $212.03   $212.05   $212.00  
  Purchase #6 $239.57   10.748%   $265.319   $265.32   $265.30   $265.30  
  Purchase #7 $168.97   9.115%   $184.3716   $184.37   $184.35   $184.40  
  7 purchase totals = $1,130.33       $1,247.8311   $1,247.82   $1,247.80   $1,247.80