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	$97.54	7.157%	$104.5209	$104.52	$104.50	$104.50
Purchase #2	$19.57	6.615%	$20.8646	$20.86	$20.85	$20.90
Purchase #3	$119.46	3.615%	$123.7785	$123.78	$123.80	$123.80
Purchase #4	$132.93	7.452%	$142.8359	$142.84	$142.85	$142.80
Purchase #5	$201.41	13.508%	$228.6165	$228.62	$228.60	$228.60
Purchase #6	$8.55	7.224%	$9.1677	$9.17	$9.15	$9.20
Purchase #7	$141.48	6.607%	$150.8276	$150.83	$150.85	$150.80
7 purchase totals =	$720.94		$780.6117	$780.62	$780.60	$780.60