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 $72.30   5.194%   $76.0553   $76.06   $76.05   $76.10  
  Purchase #2 $176.30   9.679%   $193.3641   $193.36   $193.35   $193.40  
  Purchase #3 $6.44   13.251%   $7.2934   $7.29   $7.30   $7.30  
  Purchase #4 $111.72   7.186%   $119.7482   $119.75   $119.75   $119.70  
  Purchase #5 $86.77   3.189%   $89.5371   $89.54   $89.55   $89.50  
  Purchase #6 $60.64   12.447%   $68.1879   $68.19   $68.20   $68.20  
  Purchase #7 $228.57   5.785%   $241.7928   $241.79   $241.80   $241.80  
  7 purchase totals = $742.74       $795.9788   $795.98   $796.00   $796.00