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	$138.59	12.195%	$155.4911	$155.49	$155.50	$155.50
Purchase #2	$199.31	6.639%	$212.5422	$212.54	$212.55	$212.50
Purchase #3	$148.62	8.147%	$160.7281	$160.73	$160.75	$160.70
Purchase #4	$180.69	3.835%	$187.6195	$187.62	$187.60	$187.60
Purchase #5	$143.32	5.740%	$151.5466	$151.55	$151.55	$151.50
Purchase #6	$82.33	9.467%	$90.1242	$90.12	$90.10	$90.10
Purchase #7	$25.52	10.868%	$28.2935	$28.29	$28.30	$28.30
7 purchase totals =	$918.38		$986.3452	$986.34	$986.35	$986.20