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	$143.42	11.494%	$159.9047	$159.90	$159.90	$159.90
Purchase #2	$203.98	3.743%	$211.615	$211.62	$211.60	$211.60
Purchase #3	$239.71	6.192%	$254.5528	$254.55	$254.55	$254.60
Purchase #4	$101.26	8.201%	$109.5643	$109.56	$109.55	$109.60
Purchase #5	$194.44	13.573%	$220.8313	$220.83	$220.85	$220.80
Purchase #6	$148.54	11.437%	$165.5285	$165.53	$165.55	$165.50
Purchase #7	$91.42	13.659%	$103.9071	$103.91	$103.90	$103.90
7 purchase totals =	$1,122.77		$1,225.9037	$1,225.90	$1,225.90	$1,225.90