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	$100.41	3.330%	$103.7537	$103.75	$103.75	$103.80
Purchase #2	$82.39	11.530%	$91.8896	$91.89	$91.90	$91.90
Purchase #3	$212.73	10.455%	$234.9709	$234.97	$234.95	$235.00
Purchase #4	$54.87	3.322%	$56.6928	$56.69	$56.70	$56.70
Purchase #5	$117.50	9.811%	$129.0279	$129.03	$129.05	$129.00
Purchase #6	$18.98	8.203%	$20.5369	$20.54	$20.55	$20.50
Purchase #7	$229.29	11.630%	$255.9564	$255.96	$255.95	$256.00
7 purchase totals =	$816.17		$892.8282	$892.83	$892.85	$892.90