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	$94.65	11.461%	$105.4978	$105.50	$105.50	$105.50
Purchase #2	$176.67	8.236%	$191.2205	$191.22	$191.20	$191.20
Purchase #3	$78.48	4.729%	$82.1913	$82.19	$82.20	$82.20
Purchase #4	$56.93	4.336%	$59.3985	$59.40	$59.40	$59.40
Purchase #5	$113.86	11.269%	$126.6909	$126.69	$126.70	$126.70
Purchase #6	$103.49	8.512%	$112.2991	$112.30	$112.30	$112.30
Purchase #7	$141.64	8.267%	$153.3494	$153.35	$153.35	$153.30
7 purchase totals =	$765.72		$830.6475	$830.65	$830.65	$830.60