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	$81.84	8.633%	$88.9052	$88.91	$88.90	$88.90
Purchase #2	$221.30	10.118%	$243.6911	$243.69	$243.70	$243.70
Purchase #3	$143.91	4.170%	$149.911	$149.91	$149.90	$149.90
Purchase #4	$37.95	9.479%	$41.5473	$41.55	$41.55	$41.50
Purchase #5	$62.50	13.360%	$70.85	$70.85	$70.85	$70.90
Purchase #6	$148.86	13.252%	$168.5869	$168.59	$168.60	$168.60
Purchase #7	$187.33	6.167%	$198.8826	$198.88	$198.90	$198.90
7 purchase totals =	$883.69		$962.3741	$962.38	$962.40	$962.40