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	$243.25	13.695%	$276.5631	$276.56	$276.55	$276.60
Purchase #2	$124.86	12.501%	$140.4687	$140.47	$140.45	$140.50
Purchase #3	$86.90	3.462%	$89.9085	$89.91	$89.90	$89.90
Purchase #4	$196.35	4.248%	$204.6909	$204.69	$204.70	$204.70
Purchase #5	$123.51	8.647%	$134.1899	$134.19	$134.20	$134.20
Purchase #6	$87.37	10.502%	$96.5456	$96.55	$96.55	$96.50
Purchase #7	$126.67	3.481%	$131.0794	$131.08	$131.10	$131.10
7 purchase totals =	$988.91		$1,073.4461	$1,073.45	$1,073.45	$1,073.50