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	$91.77	3.870%	$95.3215	$95.32	$95.30	$95.30
Purchase #2	$42.60	9.158%	$46.5013	$46.50	$46.50	$46.50
Purchase #3	$183.90	10.549%	$203.2996	$203.30	$203.30	$203.30
Purchase #4	$169.89	12.597%	$191.291	$191.29	$191.30	$191.30
Purchase #5	$200.39	5.460%	$211.3313	$211.33	$211.35	$211.30
Purchase #6	$12.47	9.263%	$13.6251	$13.63	$13.65	$13.60
Purchase #7	$152.87	4.339%	$159.503	$159.50	$159.50	$159.50
7 purchase totals =	$853.89		$920.8728	$920.87	$920.90	$920.80