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	$130.87	8.116%	$141.4914	$141.49	$141.50	$141.50
Purchase #2	$170.50	11.281%	$189.7341	$189.73	$189.75	$189.70
Purchase #3	$183.37	4.585%	$191.7775	$191.78	$191.80	$191.80
Purchase #4	$115.84	7.163%	$124.1376	$124.14	$124.15	$124.10
Purchase #5	$112.79	9.776%	$123.8164	$123.82	$123.80	$123.80
Purchase #6	$55.63	10.457%	$61.4472	$61.45	$61.45	$61.40
Purchase #7	$92.59	10.401%	$102.2203	$102.22	$102.20	$102.20
7 purchase totals =	$861.59		$934.6245	$934.63	$934.65	$934.50