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	$166.47	3.216%	$171.8237	$171.82	$171.80	$171.80
Purchase #2	$40.65	7.302%	$43.6183	$43.62	$43.60	$43.60
Purchase #3	$180.33	11.251%	$200.6189	$200.62	$200.60	$200.60
Purchase #4	$239.86	3.743%	$248.838	$248.84	$248.85	$248.80
Purchase #5	$79.66	3.248%	$82.2474	$82.25	$82.25	$82.20
Purchase #6	$170.98	13.415%	$193.917	$193.92	$193.90	$193.90
Purchase #7	$44.61	9.467%	$48.8332	$48.83	$48.85	$48.80
7 purchase totals =	$922.56		$989.8965	$989.90	$989.85	$989.70