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	$107.91	9.480%	$118.1399	$118.14	$118.15	$118.10
Purchase #2	$43.83	3.758%	$45.4771	$45.48	$45.50	$45.50
Purchase #3	$171.97	7.626%	$185.0844	$185.08	$185.10	$185.10
Purchase #4	$87.33	10.837%	$96.794	$96.79	$96.80	$96.80
Purchase #5	$197.29	11.756%	$220.4834	$220.48	$220.50	$220.50
Purchase #6	$27.34	3.761%	$28.3683	$28.37	$28.35	$28.40
Purchase #7	$171.66	11.758%	$191.8438	$191.84	$191.85	$191.80
7 purchase totals =	$807.33		$886.1909	$886.18	$886.25	$886.20