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	$225.33	11.461%	$251.1551	$251.16	$251.15	$251.20
Purchase #2	$166.96	13.506%	$189.5096	$189.51	$189.50	$189.50
Purchase #3	$86.70	3.719%	$89.9244	$89.92	$89.90	$89.90
Purchase #4	$131.52	12.610%	$148.1047	$148.10	$148.10	$148.10
Purchase #5	$84.37	13.745%	$95.9667	$95.97	$95.95	$96.00
Purchase #6	$128.63	13.714%	$146.2703	$146.27	$146.25	$146.30
Purchase #7	$43.64	3.818%	$45.3062	$45.31	$45.30	$45.30
7 purchase totals =	$867.15		$966.2370	$966.24	$966.15	$966.30