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	$120.94	7.730%	$130.2887	$130.29	$130.30	$130.30
Purchase #2	$102.83	8.185%	$111.2466	$111.25	$111.25	$111.20
Purchase #3	$94.93	9.864%	$104.2939	$104.29	$104.30	$104.30
Purchase #4	$173.31	6.856%	$185.1921	$185.19	$185.20	$185.20
Purchase #5	$42.42	6.304%	$45.0942	$45.09	$45.10	$45.10
Purchase #6	$186.86	13.744%	$212.542	$212.54	$212.55	$212.50
Purchase #7	$58.40	7.770%	$62.9377	$62.94	$62.95	$62.90
7 purchase totals =	$779.69		$851.5952	$851.59	$851.65	$851.50