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 $186.49   3.253%   $192.5565   $192.56   $192.55   $192.60  
  Purchase #2 $30.93   11.793%   $34.5776   $34.58   $34.60   $34.60  
  Purchase #3 $178.64   11.736%   $199.6052   $199.61   $199.60   $199.60  
  Purchase #4 $196.51   11.433%   $218.977   $218.98   $219.00   $219.00  
  Purchase #5 $48.68   4.647%   $50.9422   $50.94   $50.95   $50.90  
  Purchase #6 $143.33   13.539%   $162.7354   $162.74   $162.75   $162.70  
  Purchase #7 $239.77   4.661%   $250.9457   $250.95   $250.95   $250.90  
  7 purchase totals = $1,024.35       $1,110.3396   $1,110.36   $1,110.40   $1,110.30