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	$223.44	12.604%	$251.6024	$251.60	$251.60	$251.60
Purchase #2	$247.40	12.397%	$278.0702	$278.07	$278.05	$278.10
Purchase #3	$33.34	12.819%	$37.6139	$37.61	$37.60	$37.60
Purchase #4	$38.83	9.752%	$42.6167	$42.62	$42.60	$42.60
Purchase #5	$109.72	10.282%	$121.0014	$121.00	$121.00	$121.00
Purchase #6	$123.50	6.830%	$131.9351	$131.94	$131.95	$131.90
Purchase #7	$209.25	12.135%	$234.6425	$234.64	$234.65	$234.60
7 purchase totals =	$985.48		$1,097.4822	$1,097.48	$1,097.45	$1,097.40