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	$77.34	6.704%	$82.5249	$82.52	$82.50	$82.50
Purchase #2	$115.38	13.574%	$131.0417	$131.04	$131.05	$131.00
Purchase #3	$36.86	6.857%	$39.3875	$39.39	$39.40	$39.40
Purchase #4	$181.99	12.812%	$205.3066	$205.31	$205.30	$205.30
Purchase #5	$5.81	5.629%	$6.137	$6.14	$6.15	$6.10
Purchase #6	$236.36	9.263%	$258.254	$258.25	$258.25	$258.30
Purchase #7	$89.77	11.189%	$99.8144	$99.81	$99.80	$99.80
7 purchase totals =	$743.51		$822.4661	$822.46	$822.45	$822.40