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	$160.56	13.500%	$182.2356	$182.24	$182.25	$182.20
Purchase #2	$162.49	10.245%	$179.1371	$179.14	$179.15	$179.10
Purchase #3	$60.45	11.281%	$67.2694	$67.27	$67.25	$67.30
Purchase #4	$109.44	13.235%	$123.9244	$123.92	$123.90	$123.90
Purchase #5	$236.38	5.149%	$248.5512	$248.55	$248.55	$248.60
Purchase #6	$85.78	11.333%	$95.5014	$95.50	$95.50	$95.50
Purchase #7	$225.97	12.289%	$253.7395	$253.74	$253.75	$253.70
7 purchase totals =	$1,041.07		$1,150.3586	$1,150.36	$1,150.35	$1,150.30