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	$47.34	11.325%	$52.7013	$52.70	$52.70	$52.70
Purchase #2	$32.47	8.768%	$35.317	$35.32	$35.30	$35.30
Purchase #3	$107.30	4.658%	$112.298	$112.30	$112.30	$112.30
Purchase #4	$25.61	12.742%	$28.8732	$28.87	$28.85	$28.90
Purchase #5	$114.34	8.175%	$123.6873	$123.69	$123.70	$123.70
Purchase #6	$93.64	9.469%	$102.5068	$102.51	$102.50	$102.50
Purchase #7	$75.59	13.485%	$85.7833	$85.78	$85.80	$85.80
7 purchase totals =	$496.29		$541.1669	$541.17	$541.15	$541.20