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	$73.64	10.652%	$81.4841	$81.48	$81.50	$81.50
Purchase #2	$12.86	6.275%	$13.667	$13.67	$13.65	$13.70
Purchase #3	$56.61	12.457%	$63.6619	$63.66	$63.65	$63.70
Purchase #4	$85.98	3.713%	$89.1724	$89.17	$89.15	$89.20
Purchase #5	$141.68	7.644%	$152.51	$152.51	$152.50	$152.50
Purchase #6	$69.39	9.838%	$76.2166	$76.22	$76.20	$76.20
Purchase #7	$135.32	6.219%	$143.7356	$143.74	$143.75	$143.70
7 purchase totals =	$575.48		$620.4476	$620.45	$620.40	$620.50