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	$38.50	13.647%	$43.7541	$43.75	$43.75	$43.80
Purchase #2	$249.55	7.133%	$267.3504	$267.35	$267.35	$267.40
Purchase #3	$80.26	11.382%	$89.3952	$89.40	$89.40	$89.40
Purchase #4	$126.42	12.583%	$142.3274	$142.33	$142.35	$142.30
Purchase #5	$152.96	9.199%	$167.0308	$167.03	$167.05	$167.00
Purchase #6	$161.89	6.278%	$172.0535	$172.05	$172.05	$172.10
Purchase #7	$65.72	7.695%	$70.7772	$70.78	$70.80	$70.80
7 purchase totals =	$875.30		$952.6886	$952.69	$952.75	$952.80