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	$160.66	11.729%	$179.5038	$179.50	$179.50	$179.50
Purchase #2	$91.65	7.698%	$98.7052	$98.71	$98.70	$98.70
Purchase #3	$80.98	10.318%	$89.3355	$89.34	$89.35	$89.30
Purchase #4	$173.48	9.127%	$189.3135	$189.31	$189.30	$189.30
Purchase #5	$176.76	12.402%	$198.6818	$198.68	$198.70	$198.70
Purchase #6	$88.91	11.258%	$98.9195	$98.92	$98.90	$98.90
Purchase #7	$186.74	9.806%	$205.0517	$205.05	$205.05	$205.10
7 purchase totals =	$959.18		$1,059.5110	$1,059.51	$1,059.50	$1,059.50