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	$79.82	5.182%	$83.9563	$83.96	$83.95	$84.00
Purchase #2	$245.74	12.443%	$276.3174	$276.32	$276.30	$276.30
Purchase #3	$48.38	11.508%	$53.9476	$53.95	$53.95	$53.90
Purchase #4	$48.72	9.508%	$53.3523	$53.35	$53.35	$53.40
Purchase #5	$25.72	5.276%	$27.077	$27.08	$27.10	$27.10
Purchase #6	$49.36	13.406%	$55.9772	$55.98	$56.00	$56.00
Purchase #7	$17.72	13.854%	$20.1749	$20.17	$20.15	$20.20
7 purchase totals =	$515.46		$570.8027	$570.81	$570.80	$570.90