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	$55.51	8.685%	$60.331	$60.33	$60.35	$60.30
Purchase #2	$222.64	9.225%	$243.1785	$243.18	$243.20	$243.20
Purchase #3	$57.39	7.291%	$61.5743	$61.57	$61.55	$61.60
Purchase #4	$219.67	3.658%	$227.7055	$227.71	$227.70	$227.70
Purchase #5	$202.50	10.418%	$223.5965	$223.60	$223.60	$223.60
Purchase #6	$104.93	13.299%	$118.8846	$118.88	$118.90	$118.90
Purchase #7	$79.61	12.196%	$89.3192	$89.32	$89.30	$89.30
7 purchase totals =	$942.25		$1,024.5896	$1,024.59	$1,024.60	$1,024.60