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	$79.83	13.781%	$90.8314	$90.83	$90.85	$90.80
Purchase #2	$141.50	10.760%	$156.7254	$156.73	$156.75	$156.70
Purchase #3	$207.62	3.239%	$214.3448	$214.34	$214.35	$214.30
Purchase #4	$59.83	6.692%	$63.8338	$63.83	$63.85	$63.80
Purchase #5	$223.89	12.290%	$251.4061	$251.41	$251.40	$251.40
Purchase #6	$184.66	7.328%	$198.1919	$198.19	$198.20	$198.20
Purchase #7	$78.35	6.826%	$83.6982	$83.70	$83.70	$83.70
7 purchase totals =	$975.68		$1,059.0316	$1,059.03	$1,059.10	$1,058.90