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	$226.44	11.224%	$251.8556	$251.86	$251.85	$251.90
Purchase #2	$224.89	6.581%	$239.69	$239.69	$239.70	$239.70
Purchase #3	$29.71	6.219%	$31.5577	$31.56	$31.55	$31.60
Purchase #4	$222.33	7.242%	$238.4311	$238.43	$238.45	$238.40
Purchase #5	$130.83	13.743%	$148.81	$148.81	$148.80	$148.80
Purchase #6	$87.32	6.780%	$93.2403	$93.24	$93.25	$93.20
Purchase #7	$87.40	10.828%	$96.8637	$96.86	$96.85	$96.90
7 purchase totals =	$1,008.92		$1,100.4484	$1,100.45	$1,100.45	$1,100.50