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	$204.89	10.600%	$226.6083	$226.61	$226.60	$226.60
Purchase #2	$63.56	4.328%	$66.3109	$66.31	$66.30	$66.30
Purchase #3	$213.80	4.501%	$223.4231	$223.42	$223.40	$223.40
Purchase #4	$107.86	13.360%	$122.2701	$122.27	$122.25	$122.30
Purchase #5	$139.33	6.205%	$147.9754	$147.98	$148.00	$148.00
Purchase #6	$207.46	5.621%	$219.1213	$219.12	$219.10	$219.10
Purchase #7	$92.67	8.179%	$100.2495	$100.25	$100.25	$100.20
7 purchase totals =	$1,029.57		$1,105.9586	$1,105.96	$1,105.90	$1,105.90