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	$42.44	6.774%	$45.3149	$45.31	$45.30	$45.30
Purchase #2	$239.28	11.746%	$267.3858	$267.39	$267.40	$267.40
Purchase #3	$17.25	9.360%	$18.8646	$18.86	$18.85	$18.90
Purchase #4	$164.97	12.404%	$185.4329	$185.43	$185.45	$185.40
Purchase #5	$66.28	7.769%	$71.4293	$71.43	$71.45	$71.40
Purchase #6	$14.75	12.755%	$16.6314	$16.63	$16.65	$16.60
Purchase #7	$146.72	10.632%	$162.3193	$162.32	$162.30	$162.30
7 purchase totals =	$691.69		$767.3782	$767.37	$767.40	$767.30