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	$66.30	6.498%	$70.6082	$70.61	$70.60	$70.60
Purchase #2	$202.31	9.661%	$221.8552	$221.86	$221.85	$221.90
Purchase #3	$18.39	8.796%	$20.0076	$20.01	$20.00	$20.00
Purchase #4	$76.43	13.662%	$86.8719	$86.87	$86.85	$86.90
Purchase #5	$47.87	11.557%	$53.4023	$53.40	$53.40	$53.40
Purchase #6	$245.59	12.270%	$275.7239	$275.72	$275.70	$275.70
Purchase #7	$233.48	9.757%	$256.2606	$256.26	$256.25	$256.30
7 purchase totals =	$890.37		$984.7297	$984.73	$984.65	$984.80