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	$140.89	11.767%	$157.4685	$157.47	$157.45	$157.50
Purchase #2	$151.91	8.313%	$164.5383	$164.54	$164.55	$164.50
Purchase #3	$138.90	5.794%	$146.9479	$146.95	$146.95	$146.90
Purchase #4	$88.56	7.830%	$95.4942	$95.49	$95.50	$95.50
Purchase #5	$180.31	5.148%	$189.5924	$189.59	$189.60	$189.60
Purchase #6	$24.29	11.436%	$27.0678	$27.07	$27.05	$27.10
Purchase #7	$55.34	4.658%	$57.9177	$57.92	$57.90	$57.90
7 purchase totals =	$780.20		$839.0268	$839.03	$839.00	$839.00