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	$24.45	3.860%	$25.3938	$25.39	$25.40	$25.40
Purchase #2	$135.82	7.830%	$146.4547	$146.45	$146.45	$146.50
Purchase #3	$16.43	9.786%	$18.0378	$18.04	$18.05	$18.00
Purchase #4	$41.42	9.740%	$45.4543	$45.45	$45.45	$45.50
Purchase #5	$140.61	8.324%	$152.3144	$152.31	$152.30	$152.30
Purchase #6	$208.74	6.272%	$221.8322	$221.83	$221.85	$221.80
Purchase #7	$240.36	7.869%	$259.2739	$259.27	$259.25	$259.30
7 purchase totals =	$807.83		$868.7611	$868.74	$868.75	$868.80