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	$238.39	11.403%	$265.5736	$265.57	$265.55	$265.60
Purchase #2	$137.76	8.824%	$149.9159	$149.92	$149.90	$149.90
Purchase #3	$184.80	8.180%	$199.9166	$199.92	$199.90	$199.90
Purchase #4	$92.59	3.796%	$96.1047	$96.10	$96.10	$96.10
Purchase #5	$96.92	6.387%	$103.1103	$103.11	$103.10	$103.10
Purchase #6	$83.46	7.385%	$89.6235	$89.62	$89.60	$89.60
Purchase #7	$97.94	5.702%	$103.5245	$103.52	$103.50	$103.50
7 purchase totals =	$931.86		$1,007.7691	$1,007.76	$1,007.65	$1,007.70