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	$16.57	8.404%	$17.9625	$17.96	$17.95	$18.00
Purchase #2	$238.88	10.484%	$263.9242	$263.92	$263.90	$263.90
Purchase #3	$92.25	4.570%	$96.4658	$96.47	$96.45	$96.50
Purchase #4	$100.67	8.368%	$109.0941	$109.09	$109.10	$109.10
Purchase #5	$59.38	13.361%	$67.3138	$67.31	$67.30	$67.30
Purchase #6	$219.48	8.504%	$238.1446	$238.14	$238.15	$238.10
Purchase #7	$208.52	13.767%	$237.2269	$237.23	$237.25	$237.20
7 purchase totals =	$935.75		$1,030.1319	$1,030.12	$1,030.10	$1,030.10