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	$12.36	5.649%	$13.0582	$13.06	$13.05	$13.10
Purchase #2	$46.54	11.602%	$51.9396	$51.94	$51.95	$51.90
Purchase #3	$181.87	9.601%	$199.3313	$199.33	$199.35	$199.30
Purchase #4	$48.72	12.605%	$54.8612	$54.86	$54.85	$54.90
Purchase #5	$244.39	5.293%	$257.3256	$257.33	$257.35	$257.30
Purchase #6	$166.61	7.814%	$179.6289	$179.63	$179.65	$179.60
Purchase #7	$216.29	13.427%	$245.3313	$245.33	$245.35	$245.30
7 purchase totals =	$916.78		$1,001.4761	$1,001.48	$1,001.55	$1,001.40