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	$57.29	3.542%	$59.3192	$59.32	$59.30	$59.30
Purchase #2	$173.90	3.846%	$180.5882	$180.59	$180.60	$180.60
Purchase #3	$174.32	12.805%	$196.6417	$196.64	$196.65	$196.60
Purchase #4	$131.61	11.486%	$146.7267	$146.73	$146.75	$146.70
Purchase #5	$39.27	12.472%	$44.1678	$44.17	$44.15	$44.20
Purchase #6	$17.48	12.544%	$19.6727	$19.67	$19.65	$19.70
Purchase #7	$29.33	11.607%	$32.7343	$32.73	$32.75	$32.70
7 purchase totals =	$623.20		$679.8506	$679.85	$679.85	$679.80