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	$123.28	13.232%	$139.5924	$139.59	$139.60	$139.60
Purchase #2	$55.69	11.170%	$61.9106	$61.91	$61.90	$61.90
Purchase #3	$108.46	8.600%	$117.7876	$117.79	$117.80	$117.80
Purchase #4	$160.80	11.345%	$179.0428	$179.04	$179.05	$179.00
Purchase #5	$135.34	8.644%	$147.0388	$147.04	$147.05	$147.00
Purchase #6	$34.51	13.753%	$39.2562	$39.26	$39.25	$39.30
Purchase #7	$154.88	11.110%	$172.0872	$172.09	$172.10	$172.10
7 purchase totals =	$772.96		$856.7156	$856.72	$856.75	$856.70