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	$18.87	13.682%	$21.4518	$21.45	$21.45	$21.50
Purchase #2	$78.39	6.267%	$83.3027	$83.30	$83.30	$83.30
Purchase #3	$41.73	6.765%	$44.553	$44.55	$44.55	$44.60
Purchase #4	$40.58	9.702%	$44.5171	$44.52	$44.50	$44.50
Purchase #5	$228.66	5.809%	$241.9429	$241.94	$241.95	$241.90
Purchase #6	$208.75	10.764%	$231.2199	$231.22	$231.20	$231.20
Purchase #7	$113.51	12.168%	$127.3219	$127.32	$127.30	$127.30
7 purchase totals =	$730.49		$794.3093	$794.30	$794.25	$794.30