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	$94.61	6.634%	$100.8864	$100.89	$100.90	$100.90
Purchase #2	$245.72	10.642%	$271.8695	$271.87	$271.85	$271.90
Purchase #3	$157.36	7.214%	$168.712	$168.71	$168.70	$168.70
Purchase #4	$139.69	10.764%	$154.7262	$154.73	$154.75	$154.70
Purchase #5	$150.92	8.809%	$164.2145	$164.21	$164.20	$164.20
Purchase #6	$86.76	4.750%	$90.8811	$90.88	$90.90	$90.90
Purchase #7	$107.71	3.702%	$111.6974	$111.70	$111.70	$111.70
7 purchase totals =	$982.77		$1,062.9871	$1,062.99	$1,063.00	$1,063.00