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	$8.46	3.380%	$8.7459	$8.75	$8.75	$8.70
Purchase #2	$133.52	10.444%	$147.4648	$147.46	$147.45	$147.50
Purchase #3	$84.60	13.821%	$96.2926	$96.29	$96.30	$96.30
Purchase #4	$20.57	3.477%	$21.2852	$21.29	$21.30	$21.30
Purchase #5	$176.52	4.810%	$185.0106	$185.01	$185.00	$185.00
Purchase #6	$168.36	13.658%	$191.3546	$191.35	$191.35	$191.40
Purchase #7	$148.35	5.366%	$156.3105	$156.31	$156.30	$156.30
7 purchase totals =	$740.38		$806.4642	$806.46	$806.45	$806.50