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	$79.51	12.388%	$89.3597	$89.36	$89.35	$89.40
Purchase #2	$61.86	4.132%	$64.4161	$64.42	$64.40	$64.40
Purchase #3	$214.71	6.596%	$228.8723	$228.87	$228.85	$228.90
Purchase #4	$107.64	10.241%	$118.6634	$118.66	$118.65	$118.70
Purchase #5	$170.60	12.181%	$191.3808	$191.38	$191.40	$191.40
Purchase #6	$176.73	13.642%	$200.8395	$200.84	$200.85	$200.80
Purchase #7	$233.96	4.786%	$245.1573	$245.16	$245.15	$245.20
7 purchase totals =	$1,045.01		$1,138.6891	$1,138.69	$1,138.65	$1,138.80