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	$122.35	7.421%	$131.4296	$131.43	$131.45	$131.40
Purchase #2	$238.56	10.141%	$262.7524	$262.75	$262.75	$262.80
Purchase #3	$23.78	4.485%	$24.8465	$24.85	$24.85	$24.80
Purchase #4	$58.42	4.755%	$61.1979	$61.20	$61.20	$61.20
Purchase #5	$80.88	3.237%	$83.4981	$83.50	$83.50	$83.50
Purchase #6	$103.41	3.347%	$106.8711	$106.87	$106.85	$106.90
Purchase #7	$109.61	4.839%	$114.914	$114.91	$114.90	$114.90
7 purchase totals =	$737.01		$785.5096	$785.51	$785.50	$785.50