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	$220.97	3.772%	$229.305	$229.31	$229.30	$229.30
Purchase #2	$105.98	5.132%	$111.4189	$111.42	$111.40	$111.40
Purchase #3	$89.54	11.172%	$99.5434	$99.54	$99.55	$99.50
Purchase #4	$159.36	5.513%	$168.1455	$168.15	$168.15	$168.10
Purchase #5	$121.47	6.474%	$129.334	$129.33	$129.35	$129.30
Purchase #6	$57.37	3.364%	$59.2999	$59.30	$59.30	$59.30
Purchase #7	$214.35	13.564%	$243.4244	$243.42	$243.40	$243.40
7 purchase totals =	$969.04		$1,040.4711	$1,040.47	$1,040.45	$1,040.30