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	$156.84	8.320%	$169.8891	$169.89	$169.90	$169.90
Purchase #2	$60.59	11.757%	$67.7136	$67.71	$67.70	$67.70
Purchase #3	$176.44	5.387%	$185.9448	$185.94	$185.95	$185.90
Purchase #4	$243.55	6.166%	$258.5673	$258.57	$258.55	$258.60
Purchase #5	$151.68	10.630%	$167.8036	$167.80	$167.80	$167.80
Purchase #6	$225.33	13.594%	$255.9614	$255.96	$255.95	$256.00
Purchase #7	$217.45	11.580%	$242.6307	$242.63	$242.65	$242.60
7 purchase totals =	$1,231.88		$1,348.5105	$1,348.50	$1,348.50	$1,348.50