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	$164.85	9.641%	$180.7432	$180.74	$180.75	$180.70
Purchase #2	$31.86	12.516%	$35.8476	$35.85	$35.85	$35.80
Purchase #3	$133.57	13.464%	$151.5539	$151.55	$151.55	$151.60
Purchase #4	$172.93	13.867%	$196.9102	$196.91	$196.90	$196.90
Purchase #5	$132.71	11.524%	$148.0035	$148.00	$148.00	$148.00
Purchase #6	$144.86	5.662%	$153.062	$153.06	$153.05	$153.10
Purchase #7	$110.46	4.838%	$115.8041	$115.80	$115.80	$115.80
7 purchase totals =	$891.24		$981.9245	$981.91	$981.90	$981.90