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	$235.63	13.475%	$267.3811	$267.38	$267.40	$267.40
Purchase #2	$89.64	11.677%	$100.1073	$100.11	$100.10	$100.10
Purchase #3	$131.70	11.385%	$146.694	$146.69	$146.70	$146.70
Purchase #4	$145.56	8.132%	$157.3969	$157.40	$157.40	$157.40
Purchase #5	$218.49	13.716%	$248.4581	$248.46	$248.45	$248.50
Purchase #6	$94.54	9.357%	$103.3861	$103.39	$103.40	$103.40
Purchase #7	$226.45	10.722%	$250.73	$250.73	$250.75	$250.70
7 purchase totals =	$1,142.01		$1,274.1535	$1,274.16	$1,274.20	$1,274.20