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	$155.58	3.384%	$160.8448	$160.84	$160.85	$160.80
Purchase #2	$246.47	5.451%	$259.9051	$259.91	$259.90	$259.90
Purchase #3	$109.67	3.762%	$113.7958	$113.80	$113.80	$113.80
Purchase #4	$56.63	5.526%	$59.7594	$59.76	$59.75	$59.80
Purchase #5	$99.29	5.467%	$104.7182	$104.72	$104.70	$104.70
Purchase #6	$36.61	10.408%	$40.4204	$40.42	$40.40	$40.40
Purchase #7	$38.93	8.150%	$42.1028	$42.10	$42.10	$42.10
7 purchase totals =	$743.18		$781.5465	$781.55	$781.50	$781.50