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	$121.93	4.807%	$127.7912	$127.79	$127.80	$127.80
Purchase #2	$94.47	8.487%	$102.4877	$102.49	$102.50	$102.50
Purchase #3	$147.35	4.461%	$153.9233	$153.92	$153.90	$153.90
Purchase #4	$232.59	11.383%	$259.0657	$259.07	$259.05	$259.10
Purchase #5	$51.96	4.471%	$54.2831	$54.28	$54.30	$54.30
Purchase #6	$238.55	12.118%	$267.4575	$267.46	$267.45	$267.50
Purchase #7	$103.29	10.421%	$114.0539	$114.05	$114.05	$114.10
7 purchase totals =	$990.14		$1,079.0624	$1,079.06	$1,079.05	$1,079.20