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	$198.25	10.700%	$219.4628	$219.46	$219.45	$219.50
Purchase #2	$56.74	4.207%	$59.1271	$59.13	$59.15	$59.10
Purchase #3	$25.93	13.679%	$29.477	$29.48	$29.50	$29.50
Purchase #4	$124.70	11.609%	$139.1764	$139.18	$139.20	$139.20
Purchase #5	$239.97	9.335%	$262.3712	$262.37	$262.35	$262.40
Purchase #6	$63.95	7.121%	$68.5039	$68.50	$68.50	$68.50
Purchase #7	$54.33	12.331%	$61.0294	$61.03	$61.05	$61.00
7 purchase totals =	$763.87		$839.1478	$839.15	$839.20	$839.20