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	$18.30	5.862%	$19.3727	$19.37	$19.35	$19.40
Purchase #2	$155.93	4.486%	$162.925	$162.93	$162.95	$162.90
Purchase #3	$77.44	10.173%	$85.318	$85.32	$85.30	$85.30
Purchase #4	$190.83	12.782%	$215.2219	$215.22	$215.20	$215.20
Purchase #5	$237.47	7.746%	$255.8644	$255.86	$255.85	$255.90
Purchase #6	$44.54	6.300%	$47.346	$47.35	$47.35	$47.30
Purchase #7	$150.55	3.692%	$156.1083	$156.11	$156.10	$156.10
7 purchase totals =	$875.06		$942.1563	$942.16	$942.10	$942.10