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	$98.28	5.740%	$103.9213	$103.92	$103.90	$103.90
Purchase #2	$148.76	4.344%	$155.2221	$155.22	$155.20	$155.20
Purchase #3	$109.69	3.851%	$113.9142	$113.91	$113.90	$113.90
Purchase #4	$135.32	6.721%	$144.4149	$144.41	$144.40	$144.40
Purchase #5	$9.55	13.734%	$10.8616	$10.86	$10.85	$10.90
Purchase #6	$246.96	3.567%	$255.7691	$255.77	$255.75	$255.80
Purchase #7	$29.71	5.394%	$31.3126	$31.31	$31.30	$31.30
7 purchase totals =	$778.27		$815.4158	$815.40	$815.30	$815.40