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	$31.57	11.182%	$35.1002	$35.10	$35.10	$35.10
Purchase #2	$98.80	11.236%	$109.9012	$109.90	$109.90	$109.90
Purchase #3	$159.77	6.324%	$169.8739	$169.87	$169.85	$169.90
Purchase #4	$54.31	4.110%	$56.5421	$56.54	$56.55	$56.50
Purchase #5	$189.57	10.140%	$208.7924	$208.79	$208.80	$208.80
Purchase #6	$142.28	6.570%	$151.6278	$151.63	$151.65	$151.60
Purchase #7	$64.58	12.869%	$72.8908	$72.89	$72.90	$72.90
7 purchase totals =	$740.88		$804.7284	$804.72	$804.75	$804.70