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	$55.28	8.374%	$59.9091	$59.91	$59.90	$59.90
Purchase #2	$170.68	13.848%	$194.3158	$194.32	$194.30	$194.30
Purchase #3	$92.90	8.155%	$100.476	$100.48	$100.50	$100.50
Purchase #4	$171.89	12.607%	$193.5602	$193.56	$193.55	$193.60
Purchase #5	$188.94	11.702%	$211.0498	$211.05	$211.05	$211.00
Purchase #6	$232.93	6.129%	$247.2063	$247.21	$247.20	$247.20
Purchase #7	$51.94	11.592%	$57.9609	$57.96	$57.95	$58.00
7 purchase totals =	$964.56		$1,064.4781	$1,064.49	$1,064.45	$1,064.50