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	$81.28	10.736%	$90.0062	$90.01	$90.00	$90.00
Purchase #2	$41.72	11.653%	$46.5816	$46.58	$46.60	$46.60
Purchase #3	$158.35	6.716%	$168.9848	$168.98	$169.00	$169.00
Purchase #4	$159.41	6.417%	$169.6393	$169.64	$169.65	$169.60
Purchase #5	$28.51	12.377%	$32.0387	$32.04	$32.05	$32.00
Purchase #6	$63.74	13.673%	$72.4552	$72.46	$72.45	$72.50
Purchase #7	$201.88	7.571%	$217.1643	$217.16	$217.15	$217.20
7 purchase totals =	$734.89		$796.8701	$796.87	$796.90	$796.90