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	$104.54	4.661%	$109.4126	$109.41	$109.40	$109.40
Purchase #2	$193.82	3.463%	$200.532	$200.53	$200.55	$200.50
Purchase #3	$59.87	3.141%	$61.7505	$61.75	$61.75	$61.80
Purchase #4	$165.72	9.176%	$180.9265	$180.93	$180.95	$180.90
Purchase #5	$39.61	6.636%	$42.2385	$42.24	$42.25	$42.20
Purchase #6	$175.73	8.613%	$190.8656	$190.87	$190.85	$190.90
Purchase #7	$40.84	3.123%	$42.1154	$42.12	$42.10	$42.10
7 purchase totals =	$780.13		$827.8411	$827.85	$827.85	$827.80