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	$223.33	12.757%	$251.8202	$251.82	$251.80	$251.80
Purchase #2	$48.72	10.318%	$53.7469	$53.75	$53.75	$53.70
Purchase #3	$162.38	13.269%	$183.9262	$183.93	$183.95	$183.90
Purchase #4	$7.40	6.666%	$7.8933	$7.89	$7.90	$7.90
Purchase #5	$156.86	5.673%	$165.7587	$165.76	$165.75	$165.80
Purchase #6	$52.94	4.265%	$55.1979	$55.20	$55.20	$55.20
Purchase #7	$58.48	6.221%	$62.118	$62.12	$62.10	$62.10
7 purchase totals =	$710.11		$780.4612	$780.47	$780.45	$780.40