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	$20.93	13.611%	$23.7788	$23.78	$23.80	$23.80
Purchase #2	$154.38	3.148%	$159.2399	$159.24	$159.25	$159.20
Purchase #3	$122.60	6.361%	$130.3986	$130.40	$130.40	$130.40
Purchase #4	$65.41	11.384%	$72.8563	$72.86	$72.85	$72.90
Purchase #5	$231.45	4.741%	$242.423	$242.42	$242.40	$242.40
Purchase #6	$35.36	7.358%	$37.9618	$37.96	$37.95	$38.00
Purchase #7	$200.64	11.529%	$223.7718	$223.77	$223.75	$223.80
7 purchase totals =	$830.77		$890.4302	$890.43	$890.40	$890.50