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	$165.73	13.798%	$188.5974	$188.60	$188.60	$188.60
Purchase #2	$54.68	5.668%	$57.7793	$57.78	$57.80	$57.80
Purchase #3	$170.32	7.152%	$182.5013	$182.50	$182.50	$182.50
Purchase #4	$179.72	9.865%	$197.4494	$197.45	$197.45	$197.40
Purchase #5	$116.32	8.650%	$126.3817	$126.38	$126.40	$126.40
Purchase #6	$9.62	3.140%	$9.9221	$9.92	$9.90	$9.90
Purchase #7	$35.50	5.635%	$37.5004	$37.50	$37.50	$37.50
7 purchase totals =	$731.89		$800.1316	$800.13	$800.15	$800.10