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	$213.69	12.486%	$240.3713	$240.37	$240.35	$240.40
Purchase #2	$178.38	12.542%	$200.7524	$200.75	$200.75	$200.80
Purchase #3	$98.89	13.444%	$112.1848	$112.18	$112.20	$112.20
Purchase #4	$145.46	11.113%	$161.625	$161.63	$161.65	$161.60
Purchase #5	$233.79	3.866%	$242.8283	$242.83	$242.85	$242.80
Purchase #6	$117.90	9.798%	$129.4518	$129.45	$129.45	$129.50
Purchase #7	$61.74	9.865%	$67.8307	$67.83	$67.85	$67.80
7 purchase totals =	$1,049.85		$1,155.0443	$1,155.04	$1,155.10	$1,155.10