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	$250.28	12.826%	$282.3809	$282.38	$282.40	$282.40
Purchase #2	$76.31	5.165%	$80.2514	$80.25	$80.25	$80.30
Purchase #3	$172.38	9.159%	$188.1683	$188.17	$188.15	$188.20
Purchase #4	$60.94	6.129%	$64.675	$64.68	$64.70	$64.70
Purchase #5	$196.43	8.348%	$212.828	$212.83	$212.85	$212.80
Purchase #6	$19.60	11.690%	$21.8912	$21.89	$21.90	$21.90
Purchase #7	$71.97	12.701%	$81.1109	$81.11	$81.10	$81.10
7 purchase totals =	$847.91		$931.3057	$931.31	$931.35	$931.40