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	$46.91	9.309%	$51.2769	$51.28	$51.30	$51.30
Purchase #2	$38.31	9.265%	$41.8594	$41.86	$41.85	$41.90
Purchase #3	$216.90	11.723%	$242.3272	$242.33	$242.35	$242.30
Purchase #4	$82.73	10.531%	$91.4423	$91.44	$91.45	$91.40
Purchase #5	$150.59	12.614%	$169.5854	$169.59	$169.60	$169.60
Purchase #6	$62.62	6.643%	$66.7798	$66.78	$66.80	$66.80
Purchase #7	$143.76	11.354%	$160.0825	$160.08	$160.10	$160.10
7 purchase totals =	$741.82		$823.3535	$823.36	$823.45	$823.40