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	$245.74	9.107%	$268.1195	$268.12	$268.10	$268.10
Purchase #2	$35.72	4.389%	$37.2878	$37.29	$37.30	$37.30
Purchase #3	$46.56	11.126%	$51.7403	$51.74	$51.75	$51.70
Purchase #4	$85.89	12.724%	$96.8186	$96.82	$96.80	$96.80
Purchase #5	$101.91	6.471%	$108.5046	$108.50	$108.50	$108.50
Purchase #6	$82.67	8.294%	$89.5266	$89.53	$89.55	$89.50
Purchase #7	$49.97	9.191%	$54.5627	$54.56	$54.55	$54.60
7 purchase totals =	$648.46		$706.5601	$706.56	$706.55	$706.50