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	$250.57	12.620%	$282.1919	$282.19	$282.20	$282.20
Purchase #2	$8.27	4.116%	$8.6104	$8.61	$8.60	$8.60
Purchase #3	$54.37	9.369%	$59.4639	$59.46	$59.45	$59.50
Purchase #4	$35.35	13.615%	$40.1629	$40.16	$40.15	$40.20
Purchase #5	$18.97	10.277%	$20.9195	$20.92	$20.90	$20.90
Purchase #6	$88.60	8.428%	$96.0672	$96.07	$96.05	$96.10
Purchase #7	$93.67	7.843%	$101.0165	$101.02	$101.00	$101.00
7 purchase totals =	$549.80		$608.4323	$608.43	$608.35	$608.50