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	$165.60	3.380%	$171.1973	$171.20	$171.20	$171.20
Purchase #2	$120.75	11.459%	$134.5867	$134.59	$134.60	$134.60
Purchase #3	$54.66	11.717%	$61.0645	$61.06	$61.05	$61.10
Purchase #4	$73.92	12.197%	$82.936	$82.94	$82.95	$82.90
Purchase #5	$141.71	8.412%	$153.6306	$153.63	$153.65	$153.60
Purchase #6	$45.69	11.706%	$51.0385	$51.04	$51.05	$51.00
Purchase #7	$138.87	3.615%	$143.8902	$143.89	$143.90	$143.90
7 purchase totals =	$741.20		$798.3438	$798.35	$798.40	$798.30