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	$90.98	10.478%	$100.5129	$100.51	$100.50	$100.50
Purchase #2	$205.38	7.776%	$221.3503	$221.35	$221.35	$221.40
Purchase #3	$227.91	8.735%	$247.8179	$247.82	$247.80	$247.80
Purchase #4	$118.87	10.666%	$131.5487	$131.55	$131.55	$131.50
Purchase #5	$128.48	8.626%	$139.5627	$139.56	$139.55	$139.60
Purchase #6	$106.57	7.555%	$114.6214	$114.62	$114.60	$114.60
Purchase #7	$127.40	11.608%	$142.1886	$142.19	$142.20	$142.20
7 purchase totals =	$1,005.59		$1,097.6025	$1,097.60	$1,097.55	$1,097.60