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	$124.41	5.281%	$130.9801	$130.98	$131.00	$131.00
Purchase #2	$233.42	4.868%	$244.7829	$244.78	$244.80	$244.80
Purchase #3	$73.37	6.686%	$78.2755	$78.28	$78.30	$78.30
Purchase #4	$114.74	7.726%	$123.6048	$123.60	$123.60	$123.60
Purchase #5	$47.83	8.320%	$51.8095	$51.81	$51.80	$51.80
Purchase #6	$97.95	4.320%	$102.1814	$102.18	$102.20	$102.20
Purchase #7	$66.76	5.302%	$70.2996	$70.30	$70.30	$70.30
7 purchase totals =	$758.48		$801.9338	$801.93	$802.00	$802.00