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	$250.60	3.389%	$259.0928	$259.09	$259.10	$259.10
Purchase #2	$42.62	7.578%	$45.8497	$45.85	$45.85	$45.80
Purchase #3	$83.59	13.137%	$94.5712	$94.57	$94.55	$94.60
Purchase #4	$151.40	8.696%	$164.5657	$164.57	$164.55	$164.60
Purchase #5	$80.52	11.403%	$89.7017	$89.70	$89.70	$89.70
Purchase #6	$199.40	5.480%	$210.3271	$210.33	$210.35	$210.30
Purchase #7	$250.79	12.174%	$281.3212	$281.32	$281.30	$281.30
7 purchase totals =	$1,058.92		$1,145.4294	$1,145.43	$1,145.40	$1,145.40