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	$35.58	6.539%	$37.9066	$37.91	$37.90	$37.90
Purchase #2	$226.28	5.247%	$238.1529	$238.15	$238.15	$238.20
Purchase #3	$94.96	3.469%	$98.2542	$98.25	$98.25	$98.30
Purchase #4	$186.61	4.338%	$194.7051	$194.71	$194.70	$194.70
Purchase #5	$100.87	10.288%	$111.2475	$111.25	$111.25	$111.20
Purchase #6	$231.30	10.254%	$255.0175	$255.02	$255.00	$255.00
Purchase #7	$55.50	9.841%	$60.9618	$60.96	$60.95	$61.00
7 purchase totals =	$931.10		$996.2456	$996.25	$996.20	$996.30