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	$85.62	4.121%	$89.1484	$89.15	$89.15	$89.10
Purchase #2	$55.40	7.400%	$59.4996	$59.50	$59.50	$59.50
Purchase #3	$235.33	7.136%	$252.1231	$252.12	$252.10	$252.10
Purchase #4	$54.65	5.183%	$57.4825	$57.48	$57.50	$57.50
Purchase #5	$117.97	8.779%	$128.3266	$128.33	$128.35	$128.30
Purchase #6	$142.33	3.685%	$147.5749	$147.57	$147.55	$147.60
Purchase #7	$5.34	12.617%	$6.0137	$6.01	$6.00	$6.00
7 purchase totals =	$696.64		$740.1688	$740.16	$740.15	$740.10