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	$119.37	12.740%	$134.5777	$134.58	$134.60	$134.60
Purchase #2	$129.58	5.604%	$136.8417	$136.84	$136.85	$136.80
Purchase #3	$172.36	8.242%	$186.5659	$186.57	$186.55	$186.60
Purchase #4	$60.59	5.313%	$63.8091	$63.81	$63.80	$63.80
Purchase #5	$136.34	11.727%	$152.3286	$152.33	$152.35	$152.30
Purchase #6	$209.68	13.849%	$238.7186	$238.72	$238.70	$238.70
Purchase #7	$178.83	9.790%	$196.3375	$196.34	$196.35	$196.30
7 purchase totals =	$1,006.75		$1,109.1791	$1,109.19	$1,109.20	$1,109.10