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	$240.92	13.669%	$273.8514	$273.85	$273.85	$273.90
Purchase #2	$123.37	6.213%	$131.035	$131.04	$131.05	$131.00
Purchase #3	$90.68	10.650%	$100.3374	$100.34	$100.35	$100.30
Purchase #4	$100.31	12.394%	$112.7424	$112.74	$112.75	$112.70
Purchase #5	$97.98	7.650%	$105.4755	$105.48	$105.50	$105.50
Purchase #6	$119.64	3.492%	$123.8178	$123.82	$123.80	$123.80
Purchase #7	$153.72	11.317%	$171.1165	$171.12	$171.10	$171.10
7 purchase totals =	$926.62		$1,018.3760	$1,018.39	$1,018.40	$1,018.30