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	$79.37	13.641%	$90.1969	$90.20	$90.20	$90.20
Purchase #2	$155.56	7.327%	$166.9579	$166.96	$166.95	$167.00
Purchase #3	$67.72	6.792%	$72.3195	$72.32	$72.30	$72.30
Purchase #4	$227.64	10.603%	$251.7767	$251.78	$251.80	$251.80
Purchase #5	$214.44	11.243%	$238.5495	$238.55	$238.55	$238.50
Purchase #6	$179.56	8.738%	$195.25	$195.25	$195.25	$195.30
Purchase #7	$226.33	10.608%	$250.3391	$250.34	$250.35	$250.30
7 purchase totals =	$1,150.62		$1,265.3896	$1,265.40	$1,265.40	$1,265.40