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	$180.56	13.335%	$204.6377	$204.64	$204.65	$204.60
Purchase #2	$150.56	12.206%	$168.9374	$168.94	$168.95	$168.90
Purchase #3	$124.98	11.838%	$139.7751	$139.78	$139.80	$139.80
Purchase #4	$160.89	3.737%	$166.9025	$166.90	$166.90	$166.90
Purchase #5	$100.73	4.719%	$105.4834	$105.48	$105.50	$105.50
Purchase #6	$206.65	4.507%	$215.9637	$215.96	$215.95	$216.00
Purchase #7	$89.26	4.860%	$93.598	$93.60	$93.60	$93.60
7 purchase totals =	$1,013.63		$1,095.2978	$1,095.30	$1,095.35	$1,095.30