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 $211.77   12.838%   $238.957   $238.96   $238.95   $239.00  
  Purchase #2 $230.96   13.470%   $262.0703   $262.07   $262.05   $262.10  
  Purchase #3 $149.64   4.441%   $156.2855   $156.29   $156.30   $156.30  
  Purchase #4 $128.99   13.522%   $146.432   $146.43   $146.45   $146.40  
  Purchase #5 $155.92   5.753%   $164.8901   $164.89   $164.90   $164.90  
  Purchase #6 $115.91   3.194%   $119.6122   $119.61   $119.60   $119.60  
  Purchase #7 $89.31   7.871%   $96.3396   $96.34   $96.35   $96.30  
  7 purchase totals = $1,082.50       $1,184.5867   $1,184.59   $1,184.60   $1,184.60