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	$151.53	8.262%	$164.0494	$164.05	$164.05	$164.00
Purchase #2	$53.61	8.786%	$58.3202	$58.32	$58.30	$58.30
Purchase #3	$29.56	13.306%	$33.4933	$33.49	$33.50	$33.50
Purchase #4	$192.28	10.160%	$211.8156	$211.82	$211.80	$211.80
Purchase #5	$120.71	10.109%	$132.9126	$132.91	$132.90	$132.90
Purchase #6	$176.61	8.537%	$191.6872	$191.69	$191.70	$191.70
Purchase #7	$132.56	13.476%	$150.4238	$150.42	$150.40	$150.40
7 purchase totals =	$856.86		$942.7021	$942.70	$942.65	$942.60