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	$238.70	4.379%	$249.1527	$249.15	$249.15	$249.20
Purchase #2	$54.36	9.609%	$59.5835	$59.58	$59.60	$59.60
Purchase #3	$84.37	6.166%	$89.5723	$89.57	$89.55	$89.60
Purchase #4	$181.73	13.496%	$206.2563	$206.26	$206.25	$206.30
Purchase #5	$100.73	6.371%	$107.1475	$107.15	$107.15	$107.10
Purchase #6	$137.41	8.119%	$148.5663	$148.57	$148.55	$148.60
Purchase #7	$38.64	11.204%	$42.9692	$42.97	$42.95	$43.00
7 purchase totals =	$835.94		$903.2478	$903.25	$903.20	$903.40