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	$148.34	12.285%	$166.5636	$166.56	$166.55	$166.60
Purchase #2	$102.72	9.838%	$112.8256	$112.83	$112.85	$112.80
Purchase #3	$131.85	5.586%	$139.2151	$139.22	$139.20	$139.20
Purchase #4	$73.71	3.759%	$76.4808	$76.48	$76.50	$76.50
Purchase #5	$202.94	10.808%	$224.8738	$224.87	$224.85	$224.90
Purchase #6	$211.99	8.181%	$229.3329	$229.33	$229.35	$229.30
Purchase #7	$148.46	9.405%	$162.4227	$162.42	$162.40	$162.40
7 purchase totals =	$1,020.01		$1,111.7145	$1,111.71	$1,111.70	$1,111.70