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	$70.81	9.305%	$77.3989	$77.40	$77.40	$77.40
Purchase #2	$86.40	3.494%	$89.4188	$89.42	$89.40	$89.40
Purchase #3	$216.79	4.404%	$226.3374	$226.34	$226.35	$226.30
Purchase #4	$179.64	11.414%	$200.1441	$200.14	$200.15	$200.10
Purchase #5	$29.34	12.841%	$33.1075	$33.11	$33.10	$33.10
Purchase #6	$72.63	10.274%	$80.092	$80.09	$80.10	$80.10
Purchase #7	$78.27	6.800%	$83.5924	$83.59	$83.60	$83.60
7 purchase totals =	$733.88		$790.0911	$790.09	$790.10	$790.00