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	$245.40	4.240%	$255.805	$255.81	$255.80	$255.80
Purchase #2	$116.46	13.468%	$132.1448	$132.14	$132.15	$132.10
Purchase #3	$88.41	6.225%	$93.9135	$93.91	$93.90	$93.90
Purchase #4	$171.84	11.161%	$191.0191	$191.02	$191.00	$191.00
Purchase #5	$159.88	13.258%	$181.0769	$181.08	$181.10	$181.10
Purchase #6	$14.40	7.569%	$15.4899	$15.49	$15.50	$15.50
Purchase #7	$93.33	11.215%	$103.797	$103.80	$103.80	$103.80
7 purchase totals =	$889.72		$973.2462	$973.25	$973.25	$973.20