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	$33.92	9.282%	$37.0685	$37.07	$37.05	$37.10
Purchase #2	$28.84	3.331%	$29.8007	$29.80	$29.80	$29.80
Purchase #3	$144.75	13.656%	$164.5171	$164.52	$164.50	$164.50
Purchase #4	$198.62	4.869%	$208.2908	$208.29	$208.30	$208.30
Purchase #5	$94.31	12.296%	$105.9064	$105.91	$105.90	$105.90
Purchase #6	$86.34	10.436%	$95.3504	$95.35	$95.35	$95.40
Purchase #7	$106.54	5.349%	$112.2388	$112.24	$112.25	$112.20
7 purchase totals =	$693.32		$753.1727	$753.18	$753.15	$753.20