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	$212.81	13.489%	$241.5159	$241.52	$241.50	$241.50
Purchase #2	$11.70	9.612%	$12.8246	$12.82	$12.80	$12.80
Purchase #3	$137.64	5.738%	$145.5378	$145.54	$145.55	$145.50
Purchase #4	$246.94	8.655%	$268.3127	$268.31	$268.30	$268.30
Purchase #5	$245.55	12.552%	$276.3714	$276.37	$276.35	$276.40
Purchase #6	$81.84	9.338%	$89.4822	$89.48	$89.50	$89.50
Purchase #7	$234.88	12.494%	$264.2259	$264.23	$264.25	$264.20
7 purchase totals =	$1,171.36		$1,298.2705	$1,298.27	$1,298.25	$1,298.20