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	$38.42	12.495%	$43.2206	$43.22	$43.20	$43.20
Purchase #2	$95.32	3.146%	$98.3188	$98.32	$98.30	$98.30
Purchase #3	$89.70	10.862%	$99.4432	$99.44	$99.45	$99.40
Purchase #4	$250.85	4.841%	$262.9936	$262.99	$263.00	$263.00
Purchase #5	$218.65	4.547%	$228.592	$228.59	$228.60	$228.60
Purchase #6	$42.49	11.115%	$47.2128	$47.21	$47.20	$47.20
Purchase #7	$72.59	7.746%	$78.2128	$78.21	$78.20	$78.20
7 purchase totals =	$808.02		$857.9938	$857.98	$857.95	$857.90