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	$219.82	13.583%	$249.6782	$249.68	$249.70	$249.70
Purchase #2	$131.75	12.626%	$148.3848	$148.38	$148.40	$148.40
Purchase #3	$17.29	13.528%	$19.629	$19.63	$19.65	$19.60
Purchase #4	$181.66	8.177%	$196.5143	$196.51	$196.50	$196.50
Purchase #5	$112.64	6.572%	$120.0427	$120.04	$120.05	$120.00
Purchase #6	$169.27	3.166%	$174.6291	$174.63	$174.65	$174.60
Purchase #7	$131.35	7.820%	$141.6216	$141.62	$141.60	$141.60
7 purchase totals =	$963.78		$1,050.4997	$1,050.49	$1,050.55	$1,050.40