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	$63.48	3.600%	$65.7653	$65.77	$65.75	$65.80
Purchase #2	$178.48	7.782%	$192.3693	$192.37	$192.35	$192.40
Purchase #3	$117.42	12.275%	$131.8333	$131.83	$131.85	$131.80
Purchase #4	$210.83	13.855%	$240.0405	$240.04	$240.05	$240.00
Purchase #5	$144.47	5.371%	$152.2295	$152.23	$152.25	$152.20
Purchase #6	$169.41	10.180%	$186.6559	$186.66	$186.65	$186.70
Purchase #7	$214.64	3.148%	$221.3969	$221.40	$221.40	$221.40
7 purchase totals =	$1,098.73		$1,190.2907	$1,190.30	$1,190.30	$1,190.30