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	$154.75	6.476%	$164.7716	$164.77	$164.75	$164.80
Purchase #2	$183.51	8.392%	$198.9102	$198.91	$198.90	$198.90
Purchase #3	$25.56	11.592%	$28.5229	$28.52	$28.50	$28.50
Purchase #4	$213.80	11.229%	$237.8076	$237.81	$237.80	$237.80
Purchase #5	$10.39	9.873%	$11.4158	$11.42	$11.40	$11.40
Purchase #6	$89.58	10.387%	$98.8847	$98.88	$98.90	$98.90
Purchase #7	$74.74	5.650%	$78.9628	$78.96	$78.95	$79.00
7 purchase totals =	$752.33		$819.2756	$819.27	$819.20	$819.30