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	$114.25	3.644%	$118.4133	$118.41	$118.40	$118.40
Purchase #2	$202.32	11.677%	$225.9449	$225.94	$225.95	$225.90
Purchase #3	$247.66	4.388%	$258.5273	$258.53	$258.55	$258.50
Purchase #4	$161.49	12.780%	$182.1284	$182.13	$182.15	$182.10
Purchase #5	$100.79	7.621%	$108.4712	$108.47	$108.45	$108.50
Purchase #6	$56.48	12.485%	$63.5315	$63.53	$63.55	$63.50
Purchase #7	$37.96	6.818%	$40.5481	$40.55	$40.55	$40.50
7 purchase totals =	$920.95		$997.5647	$997.56	$997.60	$997.40