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	$243.43	13.350%	$275.9279	$275.93	$275.95	$275.90
Purchase #2	$41.40	3.607%	$42.8933	$42.89	$42.90	$42.90
Purchase #3	$107.30	9.227%	$117.2006	$117.20	$117.20	$117.20
Purchase #4	$116.34	9.677%	$127.5982	$127.60	$127.60	$127.60
Purchase #5	$191.89	12.702%	$216.2639	$216.26	$216.25	$216.30
Purchase #6	$63.62	8.362%	$68.9399	$68.94	$68.95	$68.90
Purchase #7	$188.39	12.847%	$212.5925	$212.59	$212.60	$212.60
7 purchase totals =	$952.37		$1,061.4163	$1,061.41	$1,061.45	$1,061.40