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	$138.27	12.154%	$155.0753	$155.08	$155.10	$155.10
Purchase #2	$96.52	9.559%	$105.7463	$105.75	$105.75	$105.70
Purchase #3	$239.88	13.230%	$271.6161	$271.62	$271.60	$271.60
Purchase #4	$64.82	13.426%	$73.5227	$73.52	$73.50	$73.50
Purchase #5	$113.31	13.402%	$128.4958	$128.50	$128.50	$128.50
Purchase #6	$229.67	9.139%	$250.6595	$250.66	$250.65	$250.70
Purchase #7	$115.98	13.413%	$131.5364	$131.54	$131.55	$131.50
7 purchase totals =	$998.45		$1,116.6521	$1,116.67	$1,116.65	$1,116.60