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	$197.71	12.662%	$222.744	$222.74	$222.75	$222.70
Purchase #2	$84.42	4.391%	$88.1269	$88.13	$88.15	$88.10
Purchase #3	$38.79	6.596%	$41.3486	$41.35	$41.35	$41.30
Purchase #4	$81.67	9.320%	$89.2816	$89.28	$89.30	$89.30
Purchase #5	$11.28	9.788%	$12.3841	$12.38	$12.40	$12.40
Purchase #6	$32.47	13.872%	$36.9742	$36.97	$36.95	$37.00
Purchase #7	$146.25	4.483%	$152.8064	$152.81	$152.80	$152.80
7 purchase totals =	$592.59		$643.6658	$643.66	$643.70	$643.60