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	$25.55	10.822%	$28.315	$28.32	$28.30	$28.30
Purchase #2	$67.33	3.865%	$69.9323	$69.93	$69.95	$69.90
Purchase #3	$79.81	12.637%	$89.8956	$89.90	$89.90	$89.90
Purchase #4	$129.58	11.381%	$144.3275	$144.33	$144.35	$144.30
Purchase #5	$16.60	9.536%	$18.183	$18.18	$18.20	$18.20
Purchase #6	$33.94	8.775%	$36.9182	$36.92	$36.90	$36.90
Purchase #7	$99.40	12.604%	$111.9284	$111.93	$111.95	$111.90
7 purchase totals =	$452.21		$499.5000	$499.51	$499.55	$499.40