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	$121.29	13.523%	$137.692	$137.69	$137.70	$137.70
Purchase #2	$51.40	3.463%	$53.18	$53.18	$53.20	$53.20
Purchase #3	$203.91	5.617%	$215.3636	$215.36	$215.35	$215.40
Purchase #4	$94.75	4.668%	$99.1729	$99.17	$99.15	$99.20
Purchase #5	$9.58	13.693%	$10.8918	$10.89	$10.90	$10.90
Purchase #6	$52.31	4.310%	$54.5646	$54.56	$54.55	$54.60
Purchase #7	$98.30	6.264%	$104.4575	$104.46	$104.45	$104.50
7 purchase totals =	$631.54		$675.3224	$675.31	$675.30	$675.50