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	$28.39	12.519%	$31.9441	$31.94	$31.95	$31.90
Purchase #2	$98.82	11.111%	$109.7999	$109.80	$109.80	$109.80
Purchase #3	$118.83	7.401%	$127.6246	$127.62	$127.60	$127.60
Purchase #4	$152.67	8.174%	$165.1492	$165.15	$165.15	$165.10
Purchase #5	$220.56	13.672%	$250.715	$250.72	$250.70	$250.70
Purchase #6	$7.90	4.711%	$8.2722	$8.27	$8.25	$8.30
Purchase #7	$103.39	10.240%	$113.9771	$113.98	$114.00	$114.00
7 purchase totals =	$730.56		$807.4821	$807.48	$807.45	$807.40