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	$47.43	7.267%	$50.8767	$50.88	$50.90	$50.90
Purchase #2	$124.64	4.586%	$130.356	$130.36	$130.35	$130.40
Purchase #3	$112.80	12.221%	$126.5853	$126.59	$126.60	$126.60
Purchase #4	$59.76	11.555%	$66.6653	$66.67	$66.65	$66.70
Purchase #5	$41.53	6.202%	$44.1057	$44.11	$44.10	$44.10
Purchase #6	$219.51	6.470%	$233.7123	$233.71	$233.70	$233.70
Purchase #7	$83.89	8.357%	$90.9007	$90.90	$90.90	$90.90
7 purchase totals =	$689.56		$743.2020	$743.22	$743.20	$743.30