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	$32.94	7.419%	$35.3838	$35.38	$35.40	$35.40
Purchase #2	$206.85	4.834%	$216.8491	$216.85	$216.85	$216.80
Purchase #3	$104.41	6.290%	$110.9774	$110.98	$111.00	$111.00
Purchase #4	$37.91	4.177%	$39.4935	$39.49	$39.50	$39.50
Purchase #5	$123.85	5.331%	$130.4524	$130.45	$130.45	$130.50
Purchase #6	$91.82	4.342%	$95.8068	$95.81	$95.80	$95.80
Purchase #7	$54.28	9.301%	$59.3286	$59.33	$59.35	$59.30
7 purchase totals =	$652.06		$688.2916	$688.29	$688.35	$688.30