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	$236.36	11.490%	$263.5178	$263.52	$263.50	$263.50
Purchase #2	$57.48	3.720%	$59.6183	$59.62	$59.60	$59.60
Purchase #3	$223.89	9.426%	$244.9939	$244.99	$245.00	$245.00
Purchase #4	$41.33	5.173%	$43.468	$43.47	$43.45	$43.50
Purchase #5	$21.49	6.652%	$22.9195	$22.92	$22.90	$22.90
Purchase #6	$76.40	7.834%	$82.3852	$82.39	$82.40	$82.40
Purchase #7	$70.41	4.697%	$73.7172	$73.72	$73.70	$73.70
7 purchase totals =	$727.36		$790.6199	$790.63	$790.55	$790.60