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	$106.37	4.557%	$111.2173	$111.22	$111.20	$111.20
Purchase #2	$200.29	7.800%	$215.9126	$215.91	$215.90	$215.90
Purchase #3	$163.30	10.731%	$180.8237	$180.82	$180.80	$180.80
Purchase #4	$202.62	4.410%	$211.5555	$211.56	$211.55	$211.60
Purchase #5	$237.65	10.605%	$262.8528	$262.85	$262.85	$262.90
Purchase #6	$181.44	4.810%	$190.1673	$190.17	$190.15	$190.20
Purchase #7	$237.79	4.221%	$247.8271	$247.83	$247.85	$247.80
7 purchase totals =	$1,329.46		$1,420.3563	$1,420.36	$1,420.30	$1,420.40