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	$66.98	7.547%	$72.035	$72.04	$72.05	$72.00
Purchase #2	$76.50	13.433%	$86.7762	$86.78	$86.80	$86.80
Purchase #3	$24.25	13.799%	$27.5963	$27.60	$27.60	$27.60
Purchase #4	$65.67	6.814%	$70.1448	$70.14	$70.15	$70.10
Purchase #5	$38.86	8.118%	$42.0147	$42.01	$42.00	$42.00
Purchase #6	$62.66	7.555%	$67.394	$67.39	$67.40	$67.40
Purchase #7	$167.69	10.794%	$185.7905	$185.79	$185.80	$185.80
7 purchase totals =	$502.61		$551.7515	$551.75	$551.80	$551.70