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	$229.72	8.202%	$248.5616	$248.56	$248.55	$248.60
Purchase #2	$123.54	6.572%	$131.659	$131.66	$131.65	$131.70
Purchase #3	$42.39	13.592%	$48.1516	$48.15	$48.15	$48.20
Purchase #4	$151.72	10.533%	$167.7007	$167.70	$167.70	$167.70
Purchase #5	$224.69	8.219%	$243.1573	$243.16	$243.15	$243.20
Purchase #6	$87.25	10.281%	$96.2202	$96.22	$96.20	$96.20
Purchase #7	$40.40	7.350%	$43.3694	$43.37	$43.35	$43.40
7 purchase totals =	$899.71		$978.8198	$978.82	$978.75	$979.00