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	$174.90	3.455%	$180.9428	$180.94	$180.95	$180.90
Purchase #2	$172.87	5.808%	$182.9103	$182.91	$182.90	$182.90
Purchase #3	$51.32	9.699%	$56.2975	$56.30	$56.30	$56.30
Purchase #4	$31.58	3.823%	$32.7873	$32.79	$32.80	$32.80
Purchase #5	$47.69	5.494%	$50.3101	$50.31	$50.30	$50.30
Purchase #6	$175.96	13.825%	$200.2865	$200.29	$200.30	$200.30
Purchase #7	$126.88	10.557%	$140.2747	$140.27	$140.25	$140.30
7 purchase totals =	$781.20		$843.8092	$843.81	$843.80	$843.80