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	$137.46	4.869%	$144.1529	$144.15	$144.15	$144.20
Purchase #2	$38.98	8.442%	$42.2707	$42.27	$42.25	$42.30
Purchase #3	$37.56	11.619%	$41.9241	$41.92	$41.90	$41.90
Purchase #4	$209.60	4.568%	$219.1745	$219.17	$219.15	$219.20
Purchase #5	$122.90	8.653%	$133.5345	$133.53	$133.55	$133.50
Purchase #6	$166.54	10.134%	$183.4172	$183.42	$183.40	$183.40
Purchase #7	$67.88	5.828%	$71.836	$71.84	$71.85	$71.80
7 purchase totals =	$780.92		$836.3099	$836.30	$836.25	$836.30