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	$72.86	7.227%	$78.1256	$78.13	$78.15	$78.10
Purchase #2	$78.94	9.543%	$86.4732	$86.47	$86.45	$86.50
Purchase #3	$192.36	6.588%	$205.0327	$205.03	$205.05	$205.00
Purchase #4	$13.99	7.667%	$15.0626	$15.06	$15.05	$15.10
Purchase #5	$54.53	4.727%	$57.1076	$57.11	$57.10	$57.10
Purchase #6	$139.37	5.639%	$147.2291	$147.23	$147.25	$147.20
Purchase #7	$128.77	9.676%	$141.2298	$141.23	$141.25	$141.20
7 purchase totals =	$680.82		$730.2606	$730.26	$730.30	$730.20