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	$209.40	4.187%	$218.1676	$218.17	$218.15	$218.20
Purchase #2	$16.46	12.592%	$18.5326	$18.53	$18.55	$18.50
Purchase #3	$152.63	10.801%	$169.1156	$169.12	$169.10	$169.10
Purchase #4	$24.92	13.476%	$28.2782	$28.28	$28.30	$28.30
Purchase #5	$145.75	12.257%	$163.6146	$163.61	$163.60	$163.60
Purchase #6	$105.38	6.148%	$111.8588	$111.86	$111.85	$111.90
Purchase #7	$240.35	11.850%	$268.8315	$268.83	$268.85	$268.80
7 purchase totals =	$894.89		$978.3989	$978.40	$978.40	$978.40