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	$129.56	11.766%	$144.804	$144.80	$144.80	$144.80
Purchase #2	$199.98	5.601%	$211.1809	$211.18	$211.20	$211.20
Purchase #3	$190.37	9.346%	$208.162	$208.16	$208.15	$208.20
Purchase #4	$84.94	7.763%	$91.5339	$91.53	$91.55	$91.50
Purchase #5	$85.69	7.294%	$91.9402	$91.94	$91.95	$91.90
Purchase #6	$228.96	4.362%	$238.9472	$238.95	$238.95	$238.90
Purchase #7	$19.89	5.166%	$20.9175	$20.92	$20.90	$20.90
7 purchase totals =	$939.39		$1,007.4857	$1,007.48	$1,007.50	$1,007.40