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 $178.84   8.474%   $193.9949   $193.99   $194.00   $194.00  
  Purchase #2 $175.79   12.483%   $197.7339   $197.73   $197.75   $197.70  
  Purchase #3 $44.69   7.848%   $48.1973   $48.20   $48.20   $48.20  
  Purchase #4 $240.30   10.253%   $264.938   $264.94   $264.95   $264.90  
  Purchase #5 $136.81   13.381%   $155.1165   $155.12   $155.10   $155.10  
  Purchase #6 $129.72   3.587%   $134.3731   $134.37   $134.35   $134.40  
  Purchase #7 $28.26   7.825%   $30.4713   $30.47   $30.45   $30.50  
  7 purchase totals = $934.41       $1,024.8250   $1,024.82   $1,024.80   $1,024.80