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	$195.63	10.353%	$215.8836	$215.88	$215.90	$215.90
Purchase #2	$152.43	6.597%	$162.4858	$162.49	$162.50	$162.50
Purchase #3	$74.37	12.119%	$83.3829	$83.38	$83.40	$83.40
Purchase #4	$161.27	12.585%	$181.5658	$181.57	$181.55	$181.60
Purchase #5	$80.91	9.433%	$88.5422	$88.54	$88.55	$88.50
Purchase #6	$82.49	8.698%	$89.665	$89.67	$89.65	$89.70
Purchase #7	$17.30	8.193%	$18.7174	$18.72	$18.70	$18.70
7 purchase totals =	$764.40		$840.2427	$840.25	$840.25	$840.30