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	$83.88	6.463%	$89.3012	$89.30	$89.30	$89.30
Purchase #2	$32.46	7.313%	$34.8338	$34.83	$34.85	$34.80
Purchase #3	$230.56	12.732%	$259.9149	$259.91	$259.90	$259.90
Purchase #4	$152.35	9.221%	$166.3982	$166.40	$166.40	$166.40
Purchase #5	$90.97	13.665%	$103.4011	$103.40	$103.40	$103.40
Purchase #6	$243.50	13.410%	$276.1534	$276.15	$276.15	$276.20
Purchase #7	$134.56	12.447%	$151.3087	$151.31	$151.30	$151.30
7 purchase totals =	$968.28		$1,081.3113	$1,081.30	$1,081.30	$1,081.30