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	$20.51	11.680%	$22.9056	$22.91	$22.90	$22.90
Purchase #2	$168.59	8.373%	$182.706	$182.71	$182.70	$182.70
Purchase #3	$199.83	11.570%	$222.9503	$222.95	$222.95	$223.00
Purchase #4	$39.90	8.541%	$43.3079	$43.31	$43.30	$43.30
Purchase #5	$40.48	9.495%	$44.3236	$44.32	$44.30	$44.30
Purchase #6	$51.63	4.443%	$53.9239	$53.92	$53.90	$53.90
Purchase #7	$117.62	10.823%	$130.35	$130.35	$130.35	$130.40
7 purchase totals =	$638.56		$700.4673	$700.47	$700.40	$700.50