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	$98.70	10.668%	$109.2293	$109.23	$109.25	$109.20
Purchase #2	$25.89	5.253%	$27.25	$27.25	$27.25	$27.30
Purchase #3	$206.33	13.197%	$233.5594	$233.56	$233.55	$233.60
Purchase #4	$109.34	4.623%	$114.3948	$114.39	$114.40	$114.40
Purchase #5	$238.75	5.630%	$252.1916	$252.19	$252.20	$252.20
Purchase #6	$170.32	9.520%	$186.5345	$186.53	$186.55	$186.50
Purchase #7	$67.27	8.305%	$72.8568	$72.86	$72.85	$72.90
7 purchase totals =	$916.60		$996.0164	$996.01	$996.05	$996.10