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	$83.38	9.108%	$90.9743	$90.97	$90.95	$91.00
Purchase #2	$58.50	6.608%	$62.3657	$62.37	$62.35	$62.40
Purchase #3	$28.36	7.738%	$30.5545	$30.55	$30.55	$30.60
Purchase #4	$95.60	8.553%	$103.7767	$103.78	$103.80	$103.80
Purchase #5	$27.74	13.807%	$31.5701	$31.57	$31.55	$31.60
Purchase #6	$47.92	9.830%	$52.6305	$52.63	$52.65	$52.60
Purchase #7	$93.83	7.625%	$100.9845	$100.98	$101.00	$101.00
7 purchase totals =	$435.33		$472.8563	$472.85	$472.85	$473.00