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	$28.34	9.786%	$31.1134	$31.11	$31.10	$31.10
Purchase #2	$184.63	12.172%	$207.1032	$207.10	$207.10	$207.10
Purchase #3	$70.78	10.410%	$78.1482	$78.15	$78.15	$78.10
Purchase #4	$175.77	8.841%	$191.3098	$191.31	$191.30	$191.30
Purchase #5	$159.44	4.761%	$167.0309	$167.03	$167.05	$167.00
Purchase #6	$142.67	13.732%	$162.2614	$162.26	$162.25	$162.30
Purchase #7	$158.91	7.822%	$171.3399	$171.34	$171.35	$171.30
7 purchase totals =	$920.54		$1,008.3068	$1,008.30	$1,008.30	$1,008.20