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	$168.73	12.592%	$189.9765	$189.98	$190.00	$190.00
Purchase #2	$126.84	8.108%	$137.1242	$137.12	$137.10	$137.10
Purchase #3	$130.54	5.244%	$137.3855	$137.39	$137.40	$137.40
Purchase #4	$162.52	12.185%	$182.3231	$182.32	$182.30	$182.30
Purchase #5	$64.96	8.676%	$70.5959	$70.60	$70.60	$70.60
Purchase #6	$60.46	11.730%	$67.552	$67.55	$67.55	$67.60
Purchase #7	$43.49	13.662%	$49.4316	$49.43	$49.45	$49.40
7 purchase totals =	$757.54		$834.3888	$834.39	$834.40	$834.40