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	$156.73	6.288%	$166.5852	$166.59	$166.60	$166.60
Purchase #2	$65.26	7.664%	$70.2615	$70.26	$70.25	$70.30
Purchase #3	$231.39	10.829%	$256.4472	$256.45	$256.45	$256.40
Purchase #4	$158.25	4.543%	$165.4393	$165.44	$165.45	$165.40
Purchase #5	$135.48	8.142%	$146.5108	$146.51	$146.50	$146.50
Purchase #6	$209.84	11.120%	$233.1742	$233.17	$233.15	$233.20
Purchase #7	$217.94	10.182%	$240.1307	$240.13	$240.15	$240.10
7 purchase totals =	$1,174.89		$1,278.5489	$1,278.55	$1,278.55	$1,278.50