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	$108.68	12.156%	$121.8911	$121.89	$121.90	$121.90
Purchase #2	$81.25	11.273%	$90.4093	$90.41	$90.40	$90.40
Purchase #3	$142.32	4.785%	$149.13	$149.13	$149.15	$149.10
Purchase #4	$207.69	7.599%	$223.4724	$223.47	$223.45	$223.50
Purchase #5	$143.93	4.349%	$150.1895	$150.19	$150.20	$150.20
Purchase #6	$50.61	12.506%	$56.9393	$56.94	$56.95	$56.90
Purchase #7	$215.30	4.300%	$224.5579	$224.56	$224.55	$224.60
7 purchase totals =	$949.78		$1,016.5895	$1,016.59	$1,016.60	$1,016.60