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	$97.28	6.622%	$103.7219	$103.72	$103.70	$103.70
Purchase #2	$117.87	11.454%	$131.3708	$131.37	$131.35	$131.40
Purchase #3	$136.85	7.710%	$147.4011	$147.40	$147.40	$147.40
Purchase #4	$75.75	11.232%	$84.2582	$84.26	$84.25	$84.30
Purchase #5	$206.67	7.605%	$222.3873	$222.39	$222.40	$222.40
Purchase #6	$69.54	12.698%	$78.3702	$78.37	$78.35	$78.40
Purchase #7	$26.58	6.791%	$28.385	$28.39	$28.40	$28.40
7 purchase totals =	$730.54		$795.8945	$795.90	$795.85	$796.00