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	$95.94	5.181%	$100.9107	$100.91	$100.90	$100.90
Purchase #2	$135.66	9.190%	$148.1272	$148.13	$148.15	$148.10
Purchase #3	$164.42	13.433%	$186.5065	$186.51	$186.50	$186.50
Purchase #4	$205.68	11.484%	$229.3003	$229.30	$229.30	$229.30
Purchase #5	$109.59	6.300%	$116.4942	$116.49	$116.50	$116.50
Purchase #6	$209.97	8.436%	$227.6831	$227.68	$227.70	$227.70
Purchase #7	$169.56	9.341%	$185.3986	$185.40	$185.40	$185.40
7 purchase totals =	$1,090.82		$1,194.4206	$1,194.42	$1,194.45	$1,194.40