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	$69.48	10.292%	$76.6309	$76.63	$76.65	$76.60
Purchase #2	$125.91	10.570%	$139.2187	$139.22	$139.20	$139.20
Purchase #3	$77.35	9.269%	$84.5196	$84.52	$84.50	$84.50
Purchase #4	$82.52	7.380%	$88.61	$88.61	$88.60	$88.60
Purchase #5	$168.61	6.708%	$179.9204	$179.92	$179.90	$179.90
Purchase #6	$66.32	7.482%	$71.2821	$71.28	$71.30	$71.30
Purchase #7	$191.43	4.693%	$200.4138	$200.41	$200.40	$200.40
7 purchase totals =	$781.62		$840.5955	$840.59	$840.55	$840.50