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	$225.58	13.603%	$256.2656	$256.27	$256.25	$256.30
Purchase #2	$243.88	12.661%	$274.7576	$274.76	$274.75	$274.80
Purchase #3	$57.92	12.636%	$65.2388	$65.24	$65.25	$65.20
Purchase #4	$74.84	4.600%	$78.2826	$78.28	$78.30	$78.30
Purchase #5	$236.64	4.580%	$247.4781	$247.48	$247.50	$247.50
Purchase #6	$122.97	7.172%	$131.7894	$131.79	$131.80	$131.80
Purchase #7	$220.68	13.184%	$249.7745	$249.77	$249.75	$249.80
7 purchase totals =	$1,182.51		$1,303.5866	$1,303.59	$1,303.60	$1,303.70