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	$163.85	8.819%	$178.2999	$178.30	$178.30	$178.30
Purchase #2	$58.88	9.220%	$64.3087	$64.31	$64.30	$64.30
Purchase #3	$162.94	8.527%	$176.8339	$176.83	$176.85	$176.80
Purchase #4	$171.90	5.453%	$181.2737	$181.27	$181.25	$181.30
Purchase #5	$137.79	5.863%	$145.8686	$145.87	$145.85	$145.90
Purchase #6	$213.85	4.678%	$223.8539	$223.85	$223.85	$223.90
Purchase #7	$171.91	4.602%	$179.8213	$179.82	$179.80	$179.80
7 purchase totals =	$1,081.12		$1,150.2600	$1,150.25	$1,150.20	$1,150.30