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	$104.58	6.671%	$111.5565	$111.56	$111.55	$111.60
Purchase #2	$103.32	6.264%	$109.792	$109.79	$109.80	$109.80
Purchase #3	$35.29	8.565%	$38.3126	$38.31	$38.30	$38.30
Purchase #4	$199.69	12.780%	$225.2104	$225.21	$225.20	$225.20
Purchase #5	$203.66	6.464%	$216.8246	$216.82	$216.80	$216.80
Purchase #6	$37.56	4.160%	$39.1225	$39.12	$39.10	$39.10
Purchase #7	$62.84	5.115%	$66.0543	$66.05	$66.05	$66.10
7 purchase totals =	$746.94		$806.8729	$806.86	$806.80	$806.90