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	$88.98	12.872%	$100.4335	$100.43	$100.45	$100.40
Purchase #2	$101.94	9.840%	$111.9709	$111.97	$111.95	$112.00
Purchase #3	$91.84	6.719%	$98.0107	$98.01	$98.00	$98.00
Purchase #4	$67.78	6.654%	$72.2901	$72.29	$72.30	$72.30
Purchase #5	$233.82	13.671%	$265.7855	$265.79	$265.80	$265.80
Purchase #6	$204.51	8.761%	$222.4271	$222.43	$222.45	$222.40
Purchase #7	$229.27	7.780%	$247.1072	$247.11	$247.10	$247.10
7 purchase totals =	$1,018.14		$1,118.0250	$1,118.03	$1,118.05	$1,118.00