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	$226.41	9.782%	$248.5574	$248.56	$248.55	$248.60
Purchase #2	$123.94	6.863%	$132.446	$132.45	$132.45	$132.40
Purchase #3	$139.77	12.167%	$156.7758	$156.78	$156.80	$156.80
Purchase #4	$248.33	3.459%	$256.9197	$256.92	$256.90	$256.90
Purchase #5	$88.43	4.700%	$92.5862	$92.59	$92.60	$92.60
Purchase #6	$132.43	9.419%	$144.9036	$144.90	$144.90	$144.90
Purchase #7	$221.47	11.619%	$247.2026	$247.20	$247.20	$247.20
7 purchase totals =	$1,180.78		$1,279.3913	$1,279.40	$1,279.40	$1,279.40