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	$228.77	11.710%	$255.559	$255.56	$255.55	$255.60
Purchase #2	$128.69	12.408%	$144.6579	$144.66	$144.65	$144.70
Purchase #3	$223.74	9.873%	$245.8299	$245.83	$245.85	$245.80
Purchase #4	$67.57	4.175%	$70.391	$70.39	$70.40	$70.40
Purchase #5	$177.87	12.579%	$200.2443	$200.24	$200.25	$200.20
Purchase #6	$77.93	8.263%	$84.3694	$84.37	$84.35	$84.40
Purchase #7	$96.39	3.371%	$99.6393	$99.64	$99.65	$99.60
7 purchase totals =	$1,000.96		$1,100.6908	$1,100.69	$1,100.70	$1,100.70