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	$229.28	12.798%	$258.6233	$258.62	$258.60	$258.60
Purchase #2	$216.66	3.276%	$223.7578	$223.76	$223.75	$223.80
Purchase #3	$99.41	6.348%	$105.7205	$105.72	$105.70	$105.70
Purchase #4	$31.69	13.505%	$35.9697	$35.97	$35.95	$36.00
Purchase #5	$140.89	3.362%	$145.6267	$145.63	$145.65	$145.60
Purchase #6	$43.68	3.387%	$45.1594	$45.16	$45.15	$45.20
Purchase #7	$241.77	11.402%	$269.3366	$269.34	$269.35	$269.30
7 purchase totals =	$1,003.38		$1,084.1940	$1,084.20	$1,084.15	$1,084.20