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	$242.50	3.479%	$250.9366	$250.94	$250.95	$250.90
Purchase #2	$207.85	5.190%	$218.6374	$218.64	$218.65	$218.60
Purchase #3	$155.41	11.677%	$173.5572	$173.56	$173.55	$173.60
Purchase #4	$220.67	6.296%	$234.5634	$234.56	$234.55	$234.60
Purchase #5	$43.79	10.549%	$48.4094	$48.41	$48.40	$48.40
Purchase #6	$137.46	7.861%	$148.2657	$148.27	$148.25	$148.30
Purchase #7	$180.43	11.285%	$200.7915	$200.79	$200.80	$200.80
7 purchase totals =	$1,188.11		$1,275.1612	$1,275.17	$1,275.15	$1,275.20