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	$34.68	9.129%	$37.8459	$37.85	$37.85	$37.80
Purchase #2	$91.59	8.518%	$99.3916	$99.39	$99.40	$99.40
Purchase #3	$154.70	7.463%	$166.2453	$166.25	$166.25	$166.20
Purchase #4	$86.31	12.185%	$96.8269	$96.83	$96.85	$96.80
Purchase #5	$221.26	13.851%	$251.9067	$251.91	$251.90	$251.90
Purchase #6	$224.59	10.504%	$248.1809	$248.18	$248.20	$248.20
Purchase #7	$98.62	5.437%	$103.982	$103.98	$104.00	$104.00
7 purchase totals =	$911.75		$1,004.3793	$1,004.39	$1,004.45	$1,004.30