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	$222.80	12.706%	$251.109	$251.11	$251.10	$251.10
Purchase #2	$246.68	7.231%	$264.5174	$264.52	$264.50	$264.50
Purchase #3	$163.98	8.821%	$178.4447	$178.44	$178.45	$178.40
Purchase #4	$120.42	3.532%	$124.6732	$124.67	$124.65	$124.70
Purchase #5	$26.29	12.306%	$29.5252	$29.53	$29.55	$29.50
Purchase #6	$82.46	9.566%	$90.3481	$90.35	$90.35	$90.30
Purchase #7	$57.76	8.402%	$62.613	$62.61	$62.60	$62.60
7 purchase totals =	$920.39		$1,001.2306	$1,001.23	$1,001.20	$1,001.10