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	$127.69	8.474%	$138.5105	$138.51	$138.50	$138.50
Purchase #2	$221.43	8.196%	$239.5784	$239.58	$239.60	$239.60
Purchase #3	$101.36	12.348%	$113.8759	$113.88	$113.90	$113.90
Purchase #4	$58.39	11.501%	$65.1054	$65.11	$65.10	$65.10
Purchase #5	$94.79	11.779%	$105.9553	$105.96	$105.95	$106.00
Purchase #6	$218.58	13.180%	$247.3888	$247.39	$247.40	$247.40
Purchase #7	$156.61	9.522%	$171.5224	$171.52	$171.50	$171.50
7 purchase totals =	$978.85		$1,081.9367	$1,081.95	$1,081.95	$1,082.00