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 $184.85   6.859%   $197.5289   $197.53   $197.55   $197.50  
  Purchase #2 $231.98   4.208%   $241.7417   $241.74   $241.75   $241.70  
  Purchase #3 $81.97   6.410%   $87.2243   $87.22   $87.20   $87.20  
  Purchase #4 $33.44   10.811%   $37.0552   $37.06   $37.05   $37.10  
  Purchase #5 $136.62   5.853%   $144.6164   $144.62   $144.60   $144.60  
  Purchase #6 $249.98   3.212%   $258.0094   $258.01   $258.00   $258.00  
  Purchase #7 $72.82   5.641%   $76.9278   $76.93   $76.95   $76.90  
  7 purchase totals = $991.66       $1,043.1037   $1,043.11   $1,043.10   $1,043.00