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	$43.53	12.274%	$48.8729	$48.87	$48.85	$48.90
Purchase #2	$51.61	11.728%	$57.6628	$57.66	$57.65	$57.70
Purchase #3	$36.54	6.205%	$38.8073	$38.81	$38.80	$38.80
Purchase #4	$133.93	12.457%	$150.6137	$150.61	$150.60	$150.60
Purchase #5	$61.91	4.199%	$64.5096	$64.51	$64.50	$64.50
Purchase #6	$197.36	13.626%	$224.2523	$224.25	$224.25	$224.30
Purchase #7	$83.44	6.111%	$88.539	$88.54	$88.55	$88.50
7 purchase totals =	$608.32		$673.2576	$673.25	$673.20	$673.30