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	$84.34	7.708%	$90.8409	$90.84	$90.85	$90.80
Purchase #2	$188.71	6.220%	$200.4478	$200.45	$200.45	$200.40
Purchase #3	$8.71	10.666%	$9.639	$9.64	$9.65	$9.60
Purchase #4	$79.55	3.731%	$82.518	$82.52	$82.50	$82.50
Purchase #5	$44.69	6.519%	$47.6033	$47.60	$47.60	$47.60
Purchase #6	$234.66	3.242%	$242.2677	$242.27	$242.25	$242.30
Purchase #7	$125.61	10.723%	$139.0792	$139.08	$139.10	$139.10
7 purchase totals =	$766.27		$812.3959	$812.40	$812.40	$812.30