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	$200.43	6.566%	$213.5902	$213.59	$213.60	$213.60
Purchase #2	$218.38	5.630%	$230.6748	$230.67	$230.65	$230.70
Purchase #3	$243.30	6.564%	$259.2702	$259.27	$259.25	$259.30
Purchase #4	$171.79	9.615%	$188.3076	$188.31	$188.30	$188.30
Purchase #5	$80.57	11.559%	$89.8831	$89.88	$89.90	$89.90
Purchase #6	$163.77	4.183%	$170.6205	$170.62	$170.60	$170.60
Purchase #7	$183.87	6.813%	$196.3971	$196.40	$196.40	$196.40
7 purchase totals =	$1,262.11		$1,348.7435	$1,348.74	$1,348.70	$1,348.80