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	$246.88	10.482%	$272.758	$272.76	$272.75	$272.80
Purchase #2	$29.40	4.841%	$30.8233	$30.82	$30.80	$30.80
Purchase #3	$96.48	4.188%	$100.5206	$100.52	$100.50	$100.50
Purchase #4	$51.50	9.317%	$56.2983	$56.30	$56.30	$56.30
Purchase #5	$180.33	11.121%	$200.3845	$200.38	$200.40	$200.40
Purchase #6	$210.49	8.703%	$228.8089	$228.81	$228.80	$228.80
Purchase #7	$220.27	13.601%	$250.2289	$250.23	$250.25	$250.20
7 purchase totals =	$1,035.35		$1,139.8225	$1,139.82	$1,139.80	$1,139.80