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	$24.37	12.179%	$27.338	$27.34	$27.35	$27.30
Purchase #2	$167.93	9.367%	$183.66	$183.66	$183.65	$183.70
Purchase #3	$240.25	3.839%	$249.4732	$249.47	$249.45	$249.50
Purchase #4	$18.43	6.427%	$19.6145	$19.61	$19.60	$19.60
Purchase #5	$212.86	6.445%	$226.5788	$226.58	$226.60	$226.60
Purchase #6	$91.59	13.360%	$103.8264	$103.83	$103.85	$103.80
Purchase #7	$189.58	13.351%	$214.8908	$214.89	$214.90	$214.90
7 purchase totals =	$945.01		$1,025.3817	$1,025.38	$1,025.40	$1,025.40