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	$71.75	9.419%	$78.5081	$78.51	$78.50	$78.50
Purchase #2	$206.65	4.451%	$215.848	$215.85	$215.85	$215.80
Purchase #3	$168.79	3.179%	$174.1558	$174.16	$174.15	$174.20
Purchase #4	$45.47	8.594%	$49.3777	$49.38	$49.40	$49.40
Purchase #5	$106.92	7.466%	$114.9026	$114.90	$114.90	$114.90
Purchase #6	$98.33	11.251%	$109.3931	$109.39	$109.40	$109.40
Purchase #7	$224.94	13.408%	$255.1	$255.10	$255.10	$255.10
7 purchase totals =	$922.85		$997.2853	$997.29	$997.30	$997.30