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	$55.43	7.342%	$59.4997	$59.50	$59.50	$59.50
Purchase #2	$161.76	6.414%	$172.1353	$172.14	$172.15	$172.10
Purchase #3	$171.57	7.475%	$184.3949	$184.39	$184.40	$184.40
Purchase #4	$72.38	11.368%	$80.6082	$80.61	$80.60	$80.60
Purchase #5	$160.84	6.557%	$171.3863	$171.39	$171.40	$171.40
Purchase #6	$25.69	11.139%	$28.5516	$28.55	$28.55	$28.60
Purchase #7	$31.63	7.405%	$33.9722	$33.97	$33.95	$34.00
7 purchase totals =	$679.30		$730.5482	$730.55	$730.55	$730.60