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	$90.66	5.663%	$95.7941	$95.79	$95.80	$95.80
Purchase #2	$155.96	4.250%	$162.5883	$162.59	$162.60	$162.60
Purchase #3	$83.87	8.171%	$90.723	$90.72	$90.70	$90.70
Purchase #4	$38.49	11.367%	$42.8652	$42.87	$42.85	$42.90
Purchase #5	$99.86	10.165%	$110.0108	$110.01	$110.00	$110.00
Purchase #6	$219.96	11.460%	$245.1674	$245.17	$245.15	$245.20
Purchase #7	$210.32	5.281%	$221.427	$221.43	$221.45	$221.40
7 purchase totals =	$899.12		$968.5758	$968.58	$968.55	$968.60