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	$131.48	4.572%	$137.4913	$137.49	$137.50	$137.50
Purchase #2	$57.74	3.744%	$59.9018	$59.90	$59.90	$59.90
Purchase #3	$138.74	3.242%	$143.238	$143.24	$143.25	$143.20
Purchase #4	$12.69	12.476%	$14.2732	$14.27	$14.25	$14.30
Purchase #5	$79.41	6.713%	$84.7408	$84.74	$84.75	$84.70
Purchase #6	$208.58	4.358%	$217.6699	$217.67	$217.65	$217.70
Purchase #7	$82.27	9.257%	$89.8857	$89.89	$89.90	$89.90
7 purchase totals =	$710.91		$747.2007	$747.20	$747.20	$747.20