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	$41.52	12.379%	$46.6598	$46.66	$46.65	$46.70
Purchase #2	$179.33	9.421%	$196.2247	$196.22	$196.20	$196.20
Purchase #3	$28.66	7.466%	$30.7998	$30.80	$30.80	$30.80
Purchase #4	$50.93	13.630%	$57.8718	$57.87	$57.85	$57.90
Purchase #5	$150.66	5.812%	$159.4164	$159.42	$159.40	$159.40
Purchase #6	$156.92	3.450%	$162.3337	$162.33	$162.35	$162.30
Purchase #7	$151.57	10.810%	$167.9547	$167.95	$167.95	$168.00
7 purchase totals =	$759.59		$821.2609	$821.25	$821.20	$821.30