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	$167.46	5.776%	$177.1325	$177.13	$177.15	$177.10
Purchase #2	$99.27	7.618%	$106.8324	$106.83	$106.85	$106.80
Purchase #3	$43.58	5.170%	$45.8331	$45.83	$45.85	$45.80
Purchase #4	$233.74	8.731%	$254.1478	$254.15	$254.15	$254.10
Purchase #5	$80.77	12.177%	$90.6054	$90.61	$90.60	$90.60
Purchase #6	$244.91	11.568%	$273.2412	$273.24	$273.25	$273.20
Purchase #7	$183.44	7.304%	$196.8385	$196.84	$196.85	$196.80
7 purchase totals =	$1,053.17		$1,144.6309	$1,144.63	$1,144.70	$1,144.40