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	$32.33	7.840%	$34.8647	$34.86	$34.85	$34.90
Purchase #2	$108.29	5.810%	$114.5816	$114.58	$114.60	$114.60
Purchase #3	$100.76	8.445%	$109.2692	$109.27	$109.25	$109.30
Purchase #4	$129.34	6.798%	$138.1325	$138.13	$138.15	$138.10
Purchase #5	$39.30	9.371%	$42.9828	$42.98	$43.00	$43.00
Purchase #6	$83.89	13.369%	$95.1053	$95.11	$95.10	$95.10
Purchase #7	$109.41	5.515%	$115.444	$115.44	$115.45	$115.40
7 purchase totals =	$603.32		$650.3801	$650.37	$650.40	$650.40