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	$37.36	9.172%	$40.7867	$40.79	$40.80	$40.80
Purchase #2	$103.39	5.763%	$109.3484	$109.35	$109.35	$109.30
Purchase #3	$207.66	10.572%	$229.6138	$229.61	$229.60	$229.60
Purchase #4	$202.91	9.725%	$222.643	$222.64	$222.65	$222.60
Purchase #5	$59.84	12.541%	$67.3445	$67.34	$67.35	$67.30
Purchase #6	$94.62	5.429%	$99.7569	$99.76	$99.75	$99.80
Purchase #7	$154.78	4.606%	$161.9092	$161.91	$161.90	$161.90
7 purchase totals =	$860.56		$931.4025	$931.40	$931.40	$931.30