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	$114.91	12.136%	$128.8555	$128.86	$128.85	$128.90
Purchase #2	$209.76	10.319%	$231.4051	$231.41	$231.40	$231.40
Purchase #3	$96.36	4.666%	$100.8562	$100.86	$100.85	$100.90
Purchase #4	$16.34	10.410%	$18.041	$18.04	$18.05	$18.00
Purchase #5	$173.25	5.666%	$183.0663	$183.07	$183.05	$183.10
Purchase #6	$167.64	9.513%	$183.5876	$183.59	$183.60	$183.60
Purchase #7	$160.88	8.467%	$174.5017	$174.50	$174.50	$174.50
7 purchase totals =	$939.14		$1,020.3134	$1,020.33	$1,020.30	$1,020.40