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	$19.48	13.538%	$22.1172	$22.12	$22.10	$22.10
Purchase #2	$201.63	10.158%	$222.1116	$222.11	$222.10	$222.10
Purchase #3	$133.73	12.543%	$150.5038	$150.50	$150.50	$150.50
Purchase #4	$96.82	12.367%	$108.7937	$108.79	$108.80	$108.80
Purchase #5	$57.45	12.741%	$64.7697	$64.77	$64.75	$64.80
Purchase #6	$113.76	8.796%	$123.7663	$123.77	$123.75	$123.80
Purchase #7	$19.86	12.848%	$22.4116	$22.41	$22.40	$22.40
7 purchase totals =	$642.73		$714.4739	$714.47	$714.40	$714.50