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	$29.33	9.598%	$32.1451	$32.15	$32.15	$32.10
Purchase #2	$37.89	10.723%	$41.9529	$41.95	$41.95	$42.00
Purchase #3	$243.51	9.773%	$267.3082	$267.31	$267.30	$267.30
Purchase #4	$68.78	6.588%	$73.3112	$73.31	$73.30	$73.30
Purchase #5	$60.94	3.590%	$63.1277	$63.13	$63.15	$63.10
Purchase #6	$54.38	6.496%	$57.9125	$57.91	$57.90	$57.90
Purchase #7	$133.95	5.639%	$141.5034	$141.50	$141.50	$141.50
7 purchase totals =	$628.78		$677.2610	$677.26	$677.25	$677.20