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	$140.89	5.372%	$148.4586	$148.46	$148.45	$148.50
Purchase #2	$213.67	4.545%	$223.3813	$223.38	$223.40	$223.40
Purchase #3	$139.56	3.275%	$144.1306	$144.13	$144.15	$144.10
Purchase #4	$247.47	11.516%	$275.9686	$275.97	$275.95	$276.00
Purchase #5	$43.88	11.231%	$48.8082	$48.81	$48.80	$48.80
Purchase #6	$79.44	10.670%	$87.9162	$87.92	$87.90	$87.90
Purchase #7	$166.99	8.272%	$180.8034	$180.80	$180.80	$180.80
7 purchase totals =	$1,031.90		$1,109.4669	$1,109.47	$1,109.45	$1,109.50