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	$241.80	11.861%	$270.4799	$270.48	$270.50	$270.50
Purchase #2	$229.94	8.230%	$248.8641	$248.86	$248.85	$248.90
Purchase #3	$175.84	12.478%	$197.7813	$197.78	$197.80	$197.80
Purchase #4	$93.85	5.723%	$99.221	$99.22	$99.20	$99.20
Purchase #5	$39.98	6.719%	$42.6663	$42.67	$42.65	$42.70
Purchase #6	$18.85	12.773%	$21.2577	$21.26	$21.25	$21.30
Purchase #7	$121.33	8.319%	$131.4234	$131.42	$131.40	$131.40
7 purchase totals =	$921.59		$1,011.6937	$1,011.69	$1,011.65	$1,011.80