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	$227.28	9.580%	$249.0534	$249.05	$249.05	$249.10
Purchase #2	$250.74	7.171%	$268.7206	$268.72	$268.70	$268.70
Purchase #3	$126.46	10.320%	$139.5107	$139.51	$139.50	$139.50
Purchase #4	$157.79	5.698%	$166.7809	$166.78	$166.80	$166.80
Purchase #5	$116.69	3.229%	$120.4579	$120.46	$120.45	$120.50
Purchase #6	$64.76	10.207%	$71.3701	$71.37	$71.35	$71.40
Purchase #7	$112.94	13.553%	$128.2468	$128.25	$128.25	$128.20
7 purchase totals =	$1,056.66		$1,144.1404	$1,144.14	$1,144.10	$1,144.20