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	$109.89	13.305%	$124.5109	$124.51	$124.50	$124.50
Purchase #2	$243.76	7.170%	$261.2376	$261.24	$261.25	$261.20
Purchase #3	$25.97	12.300%	$29.1643	$29.16	$29.15	$29.20
Purchase #4	$150.64	3.817%	$156.3899	$156.39	$156.40	$156.40
Purchase #5	$54.79	12.201%	$61.4749	$61.47	$61.45	$61.50
Purchase #6	$148.57	11.697%	$165.9482	$165.95	$165.95	$165.90
Purchase #7	$40.81	7.385%	$43.8238	$43.82	$43.80	$43.80
7 purchase totals =	$774.43		$842.5496	$842.54	$842.50	$842.50