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	$186.28	6.383%	$198.1703	$198.17	$198.15	$198.20
Purchase #2	$96.33	8.294%	$104.3196	$104.32	$104.30	$104.30
Purchase #3	$116.81	11.666%	$130.4371	$130.44	$130.45	$130.40
Purchase #4	$69.51	12.727%	$78.3565	$78.36	$78.35	$78.40
Purchase #5	$248.64	8.154%	$268.9141	$268.91	$268.90	$268.90
Purchase #6	$211.42	10.638%	$233.9109	$233.91	$233.90	$233.90
Purchase #7	$111.26	10.709%	$123.1748	$123.17	$123.15	$123.20
7 purchase totals =	$1,040.25		$1,137.2833	$1,137.28	$1,137.20	$1,137.30