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	$178.61	9.409%	$195.4154	$195.42	$195.40	$195.40
Purchase #2	$7.54	3.706%	$7.8194	$7.82	$7.80	$7.80
Purchase #3	$40.35	3.421%	$41.7304	$41.73	$41.75	$41.70
Purchase #4	$165.74	5.648%	$175.101	$175.10	$175.10	$175.10
Purchase #5	$155.83	10.730%	$172.5506	$172.55	$172.55	$172.60
Purchase #6	$127.39	10.289%	$140.4972	$140.50	$140.50	$140.50
Purchase #7	$109.50	7.262%	$117.4519	$117.45	$117.45	$117.50
7 purchase totals =	$784.96		$850.5659	$850.57	$850.55	$850.60