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	$126.55	9.643%	$138.7532	$138.75	$138.75	$138.80
Purchase #2	$126.28	11.665%	$141.0106	$141.01	$141.00	$141.00
Purchase #3	$85.31	13.441%	$96.7765	$96.78	$96.80	$96.80
Purchase #4	$204.55	6.171%	$217.1728	$217.17	$217.15	$217.20
Purchase #5	$159.29	5.756%	$168.4587	$168.46	$168.45	$168.50
Purchase #6	$103.31	6.200%	$109.7152	$109.72	$109.70	$109.70
Purchase #7	$27.40	4.700%	$28.6878	$28.69	$28.70	$28.70
7 purchase totals =	$832.69		$900.5748	$900.58	$900.55	$900.70