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	$108.41	13.486%	$123.0302	$123.03	$123.05	$123.00
Purchase #2	$85.92	3.711%	$89.1085	$89.11	$89.10	$89.10
Purchase #3	$230.37	5.682%	$243.4596	$243.46	$243.45	$243.50
Purchase #4	$117.82	11.806%	$131.7298	$131.73	$131.75	$131.70
Purchase #5	$165.69	9.778%	$181.8912	$181.89	$181.90	$181.90
Purchase #6	$214.48	11.478%	$239.098	$239.10	$239.10	$239.10
Purchase #7	$31.56	4.841%	$33.0878	$33.09	$33.10	$33.10
7 purchase totals =	$954.25		$1,041.4051	$1,041.41	$1,041.45	$1,041.40