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	$61.31	3.362%	$63.3712	$63.37	$63.35	$63.40
Purchase #2	$83.65	7.501%	$89.9246	$89.92	$89.90	$89.90
Purchase #3	$150.59	4.496%	$157.3605	$157.36	$157.35	$157.40
Purchase #4	$125.71	9.783%	$138.0082	$138.01	$138.00	$138.00
Purchase #5	$129.64	12.307%	$145.5948	$145.59	$145.60	$145.60
Purchase #6	$54.53	8.236%	$59.0211	$59.02	$59.00	$59.00
Purchase #7	$48.56	10.179%	$53.5029	$53.50	$53.50	$53.50
7 purchase totals =	$653.99		$706.7833	$706.77	$706.70	$706.80