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	$93.59	13.196%	$105.9401	$105.94	$105.95	$105.90
Purchase #2	$100.61	7.519%	$108.1749	$108.17	$108.15	$108.20
Purchase #3	$80.78	8.777%	$87.8701	$87.87	$87.85	$87.90
Purchase #4	$79.83	11.802%	$89.2515	$89.25	$89.25	$89.30
Purchase #5	$53.65	7.613%	$57.7344	$57.73	$57.75	$57.70
Purchase #6	$191.62	9.538%	$209.8967	$209.90	$209.90	$209.90
Purchase #7	$214.34	3.712%	$222.2963	$222.30	$222.30	$222.30
7 purchase totals =	$814.42		$881.1640	$881.16	$881.15	$881.20