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	$118.25	9.560%	$129.5547	$129.55	$129.55	$129.60
Purchase #2	$156.72	11.685%	$175.0327	$175.03	$175.05	$175.00
Purchase #3	$164.40	6.200%	$174.5928	$174.59	$174.60	$174.60
Purchase #4	$235.25	5.627%	$248.4875	$248.49	$248.50	$248.50
Purchase #5	$146.64	12.745%	$165.3293	$165.33	$165.35	$165.30
Purchase #6	$51.32	10.102%	$56.5043	$56.50	$56.50	$56.50
Purchase #7	$115.57	13.650%	$131.3453	$131.35	$131.35	$131.30
7 purchase totals =	$988.15		$1,080.8466	$1,080.84	$1,080.90	$1,080.80