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	$201.77	3.774%	$209.3848	$209.38	$209.40	$209.40
Purchase #2	$107.77	10.699%	$119.3003	$119.30	$119.30	$119.30
Purchase #3	$209.56	7.436%	$225.1429	$225.14	$225.15	$225.10
Purchase #4	$188.63	3.519%	$195.2679	$195.27	$195.25	$195.30
Purchase #5	$184.73	8.258%	$199.985	$199.99	$200.00	$200.00
Purchase #6	$66.67	8.838%	$72.5623	$72.56	$72.55	$72.60
Purchase #7	$71.69	9.247%	$78.3192	$78.32	$78.30	$78.30
7 purchase totals =	$1,030.82		$1,099.9624	$1,099.96	$1,099.95	$1,100.00