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	$132.56	5.250%	$139.5194	$139.52	$139.50	$139.50
Purchase #2	$199.50	4.648%	$208.7728	$208.77	$208.75	$208.80
Purchase #3	$12.82	3.379%	$13.2532	$13.25	$13.25	$13.30
Purchase #4	$183.31	7.219%	$196.5431	$196.54	$196.55	$196.50
Purchase #5	$14.57	5.417%	$15.3593	$15.36	$15.35	$15.40
Purchase #6	$132.74	4.764%	$139.0637	$139.06	$139.05	$139.10
Purchase #7	$247.29	4.769%	$259.0833	$259.08	$259.10	$259.10
7 purchase totals =	$922.79		$971.5948	$971.58	$971.55	$971.70