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	$49.46	7.635%	$53.2363	$53.24	$53.25	$53.20
Purchase #2	$187.26	8.158%	$202.5367	$202.54	$202.55	$202.50
Purchase #3	$41.82	9.148%	$45.6457	$45.65	$45.65	$45.60
Purchase #4	$99.83	11.661%	$111.4712	$111.47	$111.45	$111.50
Purchase #5	$18.87	10.133%	$20.7821	$20.78	$20.80	$20.80
Purchase #6	$51.66	10.429%	$57.0476	$57.05	$57.05	$57.00
Purchase #7	$155.66	8.355%	$168.6654	$168.67	$168.65	$168.70
7 purchase totals =	$604.56		$659.3850	$659.40	$659.40	$659.30