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	$93.61	10.137%	$103.0992	$103.10	$103.10	$103.10
Purchase #2	$19.59	6.632%	$20.8892	$20.89	$20.90	$20.90
Purchase #3	$244.35	11.814%	$273.2175	$273.22	$273.20	$273.20
Purchase #4	$5.83	7.239%	$6.252	$6.25	$6.25	$6.30
Purchase #5	$203.90	11.379%	$227.1018	$227.10	$227.10	$227.10
Purchase #6	$32.31	3.559%	$33.4599	$33.46	$33.45	$33.50
Purchase #7	$24.72	13.772%	$28.1244	$28.12	$28.10	$28.10
7 purchase totals =	$624.31		$692.1440	$692.14	$692.10	$692.20