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	$248.65	4.369%	$259.5135	$259.51	$259.50	$259.50
Purchase #2	$234.77	13.856%	$267.2997	$267.30	$267.30	$267.30
Purchase #3	$115.61	11.323%	$128.7005	$128.70	$128.70	$128.70
Purchase #4	$147.59	12.328%	$165.7849	$165.78	$165.80	$165.80
Purchase #5	$90.95	12.166%	$102.015	$102.02	$102.00	$102.00
Purchase #6	$166.52	4.781%	$174.4813	$174.48	$174.50	$174.50
Purchase #7	$22.77	13.684%	$25.8858	$25.89	$25.90	$25.90
7 purchase totals =	$1,026.86		$1,123.6807	$1,123.68	$1,123.70	$1,123.70