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	$139.64	4.312%	$145.6613	$145.66	$145.65	$145.70
Purchase #2	$73.36	7.211%	$78.65	$78.65	$78.65	$78.70
Purchase #3	$90.96	13.648%	$103.3742	$103.37	$103.35	$103.40
Purchase #4	$244.57	10.120%	$269.3205	$269.32	$269.30	$269.30
Purchase #5	$100.38	13.181%	$113.6111	$113.61	$113.60	$113.60
Purchase #6	$70.26	3.231%	$72.5301	$72.53	$72.55	$72.50
Purchase #7	$210.32	11.346%	$234.1829	$234.18	$234.20	$234.20
7 purchase totals =	$929.49		$1,017.3301	$1,017.32	$1,017.30	$1,017.40