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	$68.64	13.650%	$78.0094	$78.01	$78.00	$78.00
Purchase #2	$100.28	10.857%	$111.1674	$111.17	$111.15	$111.20
Purchase #3	$189.33	10.585%	$209.3706	$209.37	$209.35	$209.40
Purchase #4	$119.36	10.397%	$131.7699	$131.77	$131.75	$131.80
Purchase #5	$98.87	5.431%	$104.2396	$104.24	$104.25	$104.20
Purchase #6	$175.84	8.118%	$190.1147	$190.11	$190.10	$190.10
Purchase #7	$232.85	9.825%	$255.7275	$255.73	$255.75	$255.70
7 purchase totals =	$985.17		$1,080.3991	$1,080.40	$1,080.35	$1,080.40