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	$74.69	12.259%	$83.8462	$83.85	$83.85	$83.80
Purchase #2	$128.99	13.821%	$146.8177	$146.82	$146.80	$146.80
Purchase #3	$132.78	13.794%	$151.0957	$151.10	$151.10	$151.10
Purchase #4	$17.85	13.787%	$20.311	$20.31	$20.30	$20.30
Purchase #5	$210.84	5.745%	$222.9528	$222.95	$222.95	$223.00
Purchase #6	$25.41	11.187%	$28.2526	$28.25	$28.25	$28.30
Purchase #7	$190.79	9.311%	$208.5545	$208.55	$208.55	$208.60
7 purchase totals =	$781.35		$861.8305	$861.83	$861.80	$861.90